Four stroke engine with intake manifold

ABSTRACT

The four stroke internal engine having an air intake system connected to the cylinder head and operatively connected to the intake passageway. The air intake system includes an air intake manifold having symmetrical construction with a central air passageway extending between a first end and a second end. At least one passageway extends from the central air passageway to a free end, which is operatively coupled to the intake passageway. The air intake system is usable for both a supercharged and normally aspirated engines.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application relates to and claims priority on U.S.Provisional Application No. 60/185,703, filed on Feb. 29, 2000, and U.S.Provisional Application No. 60/______, filed on Dec. 22, 2000, which areincorporated by reference herein.

FIELD OF THE INVENTION

[0002] The present invention relates generally to a new engine for usein, for example, personal watercraft. In particular, the presentinvention relates to a new four-stroke in-line engine that was developedwith a view to the future stricter environmental and emissionregulations. The engine has a flexible intake manifold that can beconfigured for use either with a supercharged engine or a normallyaspirated engine. Further, the intake manifold is configured such that aflame arrester is positioned therein to prevent the exit of flames fromthe manifold in the event of an engine backfire.

BACKGROUND OF THE INVENTION

[0003] There is a very popular type of watercraft known as a “personalwatercraft” which is designed to be operated primarily by a singlerider. Although this type of watercraft is commonly employed for singleriders, frequently provisions are made for accommodating additionalpassengers although the maximum number of passengers is more limitedthan conventional types of watercraft.

[0004] This type of watercraft is also generally quite sporting innature and normally accommodates at least the rider on a type of seat inwhich the rider sits in a straddle fashion. The passenger's area isfrequently open through the rear of the watercraft so as to facilitateentry and exit of the rider and passengers to the body of water in whichthe watercraft is operating, as this type of watercraft is normallyridden with passengers that are wearing swimming suits.

[0005] These personal watercraft are generally quite small so that theycan be conveniently transported from the owner's home to a body of waterfor its use. Because of the small size, the layout of the components isextremely critical, and this gives rise to several design considerationsthat are peculiar to this type of watercraft. However, due to itssporting nature it is also desirable if the watercraft is powered by anengine and propulsion device that are not only efficient but alsogenerate sufficient power.

[0006] Traditionally, two-cycle engines have been used to powerwatercraft, including personal watercraft. These engines have theadvantage that they are fairly powerful, relatively lightweight, andcompact.

[0007] One particular disadvantage to the two-cycle engine is itsemission content. Two-cycle engines generally exhaust larger quantitiesof hydrocarbons and other pollutants than four-cycle engines due tocylinder charging inefficiencies and the combustion of lubricating oilamong other things. When measures are taken to reduce emissions of thetwo-cycle engine, other generally undesirable consequences can result,such as an increase in the weight of the engine, a reduction of itspower output or the like. With concern for the environment andincreasingly strict emissions requirements being instituted by variousgoverning bodies. There is motivation to provide a power plant thatreduces exhaust emissions while retaining other advantageouscharacteristics such as compactness, low weight and high power output.

[0008] Four-cycle engines are commonly used as power plants in otherapplications, such as automobiles. These engines have the advantage thattheir emissions output are generally desirably lower as compared to atwo-cycle engine for a given power output.

[0009] U.S. Pat. No. 5,513,606 to Shibata, entitled “Marine PropulsionUnit” discloses several embodiments of engines of use in outboardmotors. The engines are configures such that the air induction systemsare positioned on the side of the engine.

[0010] U.S. Pat. No. 5,846,102 to Nitta et al., entitled “Four-CycleEngine For A Small Jet Boat” discloses both two and four cycle enginesfor a personal watercraft. The intake suction devices of these enginesare located on the side of the engine such that the larger four-cycleengine can be located with the personal watercraft.

[0011] These references, however, do not disclose an air intake manifoldthat is capable of being used in either a supercharged engine or anormally aspirated engine. Furthermore, these intake manifolds do notinclude a flame arrester that is positioned within the air passagewaywithin the intake manifold to prevent engine backfires from exited themanifold.

OBJECTS OF THE INVENTION

[0012] It is an object of the present invention to provide a fourstroke, in-line engine having a compact construction.

[0013] It is another object of the present invention to provide a fourstroke, in-line engine having a modular construction to permit theinterchange of parts between various engine models.

[0014] It is another object of the present invention to provide a fourstroke, in-line engine having improved exhaust emission characteristics.

[0015] It is another object of the present invention to provide a fourstroke engine having a narrow and low profile.

[0016] It is another object of the present invention to provide a fourstroke engine having a low profile valve actuation assembly forcontrolling the operation of the intake and exhaust valves.

[0017] It is another object of the present invention to provide acylinder head having a low profile to reduce engine height.

[0018] It is another object of the present invention to offset theplacement of the intake valves and exhaust valves with respect to avertical axis within the cylinder head to reduce engine height.

[0019] It is another object of the present invention to provide animproved spark plug mounting assembly for easy access within thecylinder head.

[0020] It is another object of the present invention to provide aY-shaped intake rocker arm assembly providing compact construction.

[0021] It is yet another object of the present invention to provide afour stroke engine having an improved oil collection system and oilholding tank.

[0022] It is another object to provide a four stroke engine whichcombines a closed loop cooling system and an open loop cooling systemfor enhanced cooling of the engine in accordance with the presentinvention.

[0023] It is another object to provide an open loop cooling system forcooling an exhaust manifold in accordance with the present invention,wherein the open loop cooling system enhances cooling of the crankcaseand cylinder head.

[0024] It is another object to provide an open loop cooling system forcooling an exhaust manifold in accordance with the present invention,wherein the open cooling system lowers the temperature of the exhaustmanifold such that the exhaust manifold functions as a heat sink for thecrankcase and cylinder head.

[0025] It is another object of the present invention to provide a closedloop cooling system for selectively cooling the crankcase and cylinderhead of the four stroke engine.

[0026] It is another object of the present invention to provide a closedloop cooling system having a selectively operable heat exchanger.

[0027] It is another object of the present invention to provide asupercharger for enhanced engine performance.

SUMMARY OF THE INVENTION

[0028] In accordance with the present invention, a four stroke internalcombustion engine is disclosed. The normally aspirated engine includes acrankcase and a cylinder head connected to the crankcase. The crankcaseand the cylinder head form at least one cylinder having at least oneintake valve and at least one exhaust valve. A valve actuation assemblyoperates the intake and exhaust valve. The engine includes at least oneair intake passageway operatively coupled to each cylinder through theintake valves.

[0029] The engine in accordance with the present invention includes anair intake system connected to the cylinder head and operativelyconnected to the intake passageway. The air intake system includes anair intake manifold having a central air passageway extending between afirst end and a second end. At least one passageway extends from thecentral air passageway to a free end, which is operatively coupled tothe intake passageway.

[0030] The air manifold has a generally symmetrical construction suchthat the air manifold can be used in either a normally aspirated engineor a supercharged engine. The air intake manifold includes a firstopening in the first end and a second opening in the second end. An endcap is located in one of the first opening and the second openingdepending on whether the engine is supercharged or normally aspirated.

[0031] When the four stroke internal combustion engine is a normallyaspirated engine, the air intake system includes an air inlet located atthe first opening of the air intake manifold. The end cap is located inthe second opening. A throttle is provided to regulate the flow of airinto the air intake manifold. It, however, is contemplated that acarburetor may be used. The throttle is positioned within the air intakepassageway. The throttle also includes an idle by-pass, which delivers apredetermined supply of air to the air intake system through the idleby-pass when the engine is operating in an idle operating condition. Theengine has an engine control system that is operatively connected to thethrottle. The engine control system monitors the engine operatingparameters and operates the throttle assembly in response to the engineoperating parameters.

[0032] When the four stroke internal combustion engine is a superchargedengine, a supercharger is operatively connected to the air intakesystem. With this arrangement, the supercharger is operatively connectedto the air intake manifold through the second opening in the second end.The end cap is located in the first opening. The engine control systemis operatively connected to the supercharger. The engine control systemmonitors the engine operating parameters and operates the superchargerin response to the engine operating parameters.

[0033] The engines contemplated in accordance with a fuel injectionsystem associated with the air intake system and operatively coupled tothe at least one passageway adjacent the free end. The fuel injectionsystem may include a common fuel rail extending along a top portion ofthe air intake manifold and at least one fuel injection nozzle extendingfrom the common fuel rail to the at least one passageway adjacent thefree end. The engine control system monitors engine the operatingparameters of the engine and operates the fuel injection nozzle inresponse to the engine operating parameters.

[0034] The present invention is also directed to a personal watercraftfor use by at least one passenger. The personal watercraft includes ahull, a seating assembly for the at least one passenger, and a fourstroke internal combustion engine located within the hull. It iscontemplated that the personal watercraft may have either a normallyaspirated engine or supercharged engine, as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The invention will be described in conjunction with the followingdrawings in which like reference numerals designate like elements andwherein:

[0036]FIG. 1 is a downward rear schematic perspective view of a leftside of an overhead camshaft aspirated engine in accordance with thepresent invention;

[0037]FIG. 2 is a downward rear schematic perspective view of a rightside of the engine of FIG. 1;

[0038]FIG. 3 is a downward front schematic perspective view of the leftside of the engine of FIG. 1;

[0039]FIG. 4 is a downward front schematic perspective view of the rightside of the engine of FIG. 1;

[0040]FIG. 5 is a rear end view of the engine of FIG. 1 illustrating onepossible positioning of the engine within a personal watercraft;

[0041]FIG. 6 is a downward rear schematic perspective view of avariation of the engine of FIG. 1 having a supercharger;

[0042]FIG. 7 is a rear end view of the engine of FIG. 6;

[0043]FIG. 8 is a partial cross-sectional end view of the crankcase andcylinder head housing in accordance with the present invention;

[0044]FIG. 9 is a bottom view illustrating the upper crankcase of theengine in accordance with the present invention;

[0045]FIG. 10 is a top view of the lower crankshaft illustrating thepositioning of the crankshaft and the balance shaft;

[0046]FIG. 11 is a right side partial schematic sectional view of theengine of FIG. 6;

[0047]FIG. 12 is a partial schematic sectional view of the piston,valves and valve actuator assembly in accordance with the presentinvention;

[0048]FIG. 13 is a partial overhead schematic view of the rocker armassemblies of the valve operating assembly for operating the intake andexhaust valves;

[0049]FIG. 14 is an end cross sectional view of one of the exhaustrocker arm assemblies and a portion of the intake rocker arm assemblytaken along section line 14-14 of FIG. 13;

[0050]FIG. 15 is a cross sectional view of the operative end of therocker arm assemblies showing a collapsed position of the hydraulicadjuster on the left side and an extended position of the hydraulicadjuster on the right side;

[0051]FIG. 16 is a right side cross sectional view of the valveoperating assembly located within the cylinder head having the camshaftin cross section;

[0052]FIG. 17 is another right side cross sectional view of the valveoperating assembly located within the cylinder head;

[0053]FIG. 18 is an end cross sectional view illustrating the spark plugassembly within the cylinder head;

[0054]FIG. 19 is a cross sectional view illustrating the placement ofthe cylinder head cover on the cylinder head;

[0055]FIG. 20 is a cross sectional view of the engine of FIG. 1 throughone cylinder of the engine;

[0056]FIG. 21 is a schematic perspective view of the exhaust manifold inaccordance with the present invention;

[0057]FIG. 22 is a longitudinal cross sectional view of a portion of theexhaust manifold of FIG. 21;

[0058]FIG. 23 is a side cross sectional view of a portion of the exhaustmanifold of FIG. 21;

[0059]FIG. 24 is a schematic view of the exhaust manifold and open loopcooling system in accordance with the present invention;

[0060]FIG. 25 is a schematic diagram of the cooling system for theengine in accordance with the present invention;

[0061]FIG. 26 is a rear perspective view of a right side of the airintake and fuel injection system for the engine in accordance with thepresent invention;

[0062]FIG. 27 is a cross sectional view of the air intake and fuelinjection system of FIG. 26 taken along a longitudinal axis of thesystem;

[0063]FIG. 28 is a side cross sectional view of the air intake and fuelinjection system of FIG. 26 through a swing pipe;

[0064]FIG. 29 is a variation of the air intake and fuel injection systemof FIG. 28 illustrating a cooling jacket within the swing pipe;

[0065]FIG. 30 is a front perspective view of a right side of the airintake and fuel injection system for the engine having a supercharger inaccordance with the present invention;

[0066]FIG. 31 is a cross sectional view of the air intake and fuelinjection system of FIG. 30 taken along a longitudinal axis of thesystem;

[0067]FIG. 32 is a rear view of the engine illustrating the power takeoff lid and cooling system in accordance with the present invention andthe oil filter housing in partial cross section;

[0068]FIG. 33 is a side cross sectional view of a thermostat and pumpassembly of a portion of the cooling system and a lubrication pump ofthe lubrication assembly in accordance with the present invention;

[0069]FIG. 34 is a partial schematic/partial side cross sectional viewof an oil filter unit in accordance with the present invention;

[0070]FIG. 35 is a schematic diagram illustrating the oil channel systemfor the lubrication system for the cylinder head housing;

[0071]FIG. 36 is a cross sectional side view of the power take offassembly for the engine illustrating the generator assembly inaccordance with the present invention;

[0072]FIG. 37 is another cross sectional side view of the power take offassembly for the engine illustrating the starter assembly in accordancewith the present invention;

[0073]FIG. 38 is a cross sectional side view of the power take offassembly having a supercharger for the engine in accordance with thepresent invention;

[0074]FIG. 39 is a partial schematic/partial sectional view of the camchain tensioner in accordance with the present invention;

[0075]FIG. 40 is a schematic view of the blow-by ventilation system andsuction pump in accordance with the present invention;

[0076]FIG. 41 is a schematic view of the blow-by ventilation system andsuction pump of FIG. 38 having the suction pump cover removed;

[0077]FIG. 42 is a schematic view of the engine management system forthe engine in accordance with the present invention;

[0078]FIG. 43 is a schematic perspective view of the exhaust manifoldaccording to an alternative embodiment;

[0079]FIG. 44 is a cross sectional view of a portion of the exhaustmanifold of FIG. 43;

[0080]FIG. 45 is a schematic diagram of the cooling system for theengine in accordance with the present invention for use in connectionwith the exhaust manifold of FIG. 43;

[0081]FIG. 46 is a cross sectional view of the cyclone of the blow-byventilation system;

[0082]FIG. 47 is a partial overhead cross sectional view of the engineof FIG. 6 having a cut away of the balance shaft and the power take offassembly;

[0083]FIG. 48 is an overhead view of the valve train;

[0084]FIG. 49 is a partial side cross sectional view of the balanceshaft and power take off assembly; and

[0085]FIG. 50 is a side view of the engine of FIG. 1 illustrating onepossible positioning of the engine within a personal watercraft.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0086] A four-stroke three cylinder in-line engine 1 in accordance withthe present invention is illustrated generally in FIGS. 1-4. The engine1 in accordance with the present invention will be described inconnection with a personal watercraft 5, shown in cross-section in FIG.5. A variation of the engine 1 is illustrated in FIGS. 6 and 7. Theengine 2 shown in FIGS. 6 and 7 includes a supercharger. The engines 1and 2 are adapted to be installed below a raised pedestal having aseating bench of the personal watercraft 5 inside the hull 4, as shownin FIGS. 5 and 50. With this arrangement, the oil filter cannot beplaced on the lower side of the engine or of its crankcase,respectively, if it is to be accessible for maintenance purposes becausethe hull 4 would prevent access to the oil filter. To address this, theoil filter is installed at the power take off side of the engine, to beeasily accessible from above. The access through the seating area atpresent is the only access to the engine.

[0087] While designed for use in personal watercraft, it is contemplatedthat the engine 1 (or engine 2) can be used in all terrain vehicles,snowmobiles, boats and other vehicles with minor modifications. Forexample, the cooling system for the exhaust manifold must be modifiedfor non-marine applications. Further, while the embodiments showndisclose an engine positioning with the power take off to the rear ofthe engine, the orientation can be altered to have the power take off tothe front or to the side depending on the specific vehicle or specificapplication.

Engine Configuration

[0088] The engine 1 includes a crankcase 10. A cylinder head housing 20is connected to the crankcase 10 to form a plurality of combustionchambers. The crankcase 10 and cylinder head housing 20 are inclinedwith respect to a vertical axis, as shown in FIGS. 5 and 8. Thisarrangement provides sufficient space for the air intake and fuelinjection system 40 while maintaining an overall reduced engine profile.The engines illustrated and described herein include three cylinders.The present invention, however, is not limited to three cylinders;rather, it is contemplated that a greater or fewer number of cylindersare considered to be well within the scope of the present invention. Forexample, a single cylinder version of the engine may be employed in afishing boat. Two or three cylinder versions of the engine may beemployed in a personal watercraft. A four cylinder version of the enginemay be employed in a jet boat. Four or more cylinders are considered tobe well within the scope of the present invention.

[0089] The engine 1 or 2 provides for the location of various enginecomponents including, but not limited to the starter assembly, thegenerator, the oil pump, coolant pump and other devices at one end ofthe engine in the power take off assembly 50, described below and shownin FIGS. 33, 36, 37 and 38. This unique construction and layout ofcomponents permits the use of similar parts and engine components forone, two, three and four cylinder versions of the engine. Furthermore,this arrangement permits the addition of additional cylinders on the endof the engine opposite the power take off assembly. The layout of theparts is the same. Minimal redesign of these components is necessarywhen increasing or reducing the number of cylinders.

[0090] The engine 1 contemplated herein includes an exhaust manifold 30that is secured to one side of the cylinder head housing 20 and an airintake and fuel injection system 40. The air intake and fuel injectionsystem 40 is secured to an opposite side of the cylinder head housing 20in the area above the cylinder head housing 20.

[0091] The present invention, however, is not limited to having a fuelinjection system; rather, it is contemplated that the engine can insteadbe equipped with a carburetor.

[0092] A power take off assembly 50 is located on an end of the cylinderblock 10 within the hull 4. The power take off assembly 50 defines therear side of the engine when located within the personal watercraft 5.The engine 1 or 2 further includes a lubrication system 60 as shown inFIGS. 8 and 11. The engine 1 further includes a blow-by ventilationsystem 70, as shown in FIG. 11, and an engine cooling system 80, asshown in FIG. 25.

[0093] An engine 2 is shown in FIGS. 6 and 7, which is a variation ofthe engine 1. The engine 2 has substantially the same configuration asthe engine 1. The engine 2 further includes a supercharger 90. The useof a supercharger for an engine for use in a personal watercraft is anew development, which is described in greater detail below. The engine1 can be converted with minor modification to the engine 2 having asupercharger 90. In particular, as described below, the supercharger 90is attached to an opposite end of the intake manifold 41 as compared tothe normally aspirated engine 1. The ignition and induction parametersof the engine may be modified to enhance engine performance when thesupercharger 90 is used. It is also contemplated that the compressionratio of the engine may have to be altered to accommodate thesupercharger 90. In accordance with the present invention, it iscontemplated that the engines 1 and 2 will be produced on the sameassembly line.

[0094] Because it is contemplated that the engine in accordance with thepresent invention will be used in marine applications, the exteriorsurfaces of the engines 1 or 2 will be provided with a suitable coatingto reduce corrosion and the direct exposure of the engine to theelements. The individual components of the engines 1 and 2 will now bedescribed in greater detail.

Crankcase

[0095] As illustrated in FIG. 8, the crankcase 10 contains a pluralityof passageways and compartments formed therein. Furthermore, thecrankcase 10 is formed with vertical partitions, as shown in FIGS. 9 and10, which separate the individual crank chambers, described below andexternal fins located on the crankcase 10. These vertical partitions andexternal fins increase the strength of the crankcase 10. The spacedapart vertical fins provide additional strength for an upper crankcase13 of the crankcase 10 while minimizing the weight. The verticalpartitions increase engine strength and separate the crank chambers 121in the upper and lower crankcases 12 and 13. The vertical partitionsalso secure the upper and lower crankcases together using suitablefasteners. The fasteners extend through bores in the vertical partitionsfrom a lower end of the lower crankcase to the upper crankcase. Thefasteners also serve to secure the bearings, described below, within thevertical partitions. The crankcase 10 is preferably formed from a castaluminum alloy (e.g. AlSi) for both strength and weight considerations.The crankcase 10 is preferably die cast. The present invention, however,is not limited to the use of aluminum alloys; rather, other materialsincluding but not limited to steels, alloys and composites areconsidered to be well within the scope of the present invention providedthe materials have sufficient strength for use in engine applications.

[0096] The crankcase 10 includes an upper crankcase 13 containing thecylinder block and a lower crankcase 12. A balance shaft 115 and acrankshaft 123 are located at the union between the lower crankcase 12and the upper crankcase 13. An oil tank 11 formed in a bottom portion ofthe lower crankcase 12, as shown in FIG. 8. The oil tank 11 has agenerally u-shaped configuration that partially surrounds a lowerportion of a crankcase 12. The oil tank 11 is located on both the bottomand side of the engine to house the necessary volume of oil whilemaintaining the engine's reduced profile such that oil is located on thebottom of the crankcase and the side of the crankcase 10. An interior ofthe upper crankcase 13 and the lower crankcase 12 are connected to theoil tank 11 through outlet openings 111, as shown in FIGS. 8 and 11. Achannel 112 extends from each opening 111 to an upper portion 113 formedin the lower crankcase 13. The oil collected from the crank chamber 121flows through outlet openings 111 and channels 112, then enters theupper channel portion 113 and returns to the oil tank 11. This oil thenflows under the influence of gravity downward into a lower portion 114of the oil tank 11.

[0097] A balance shaft 115 extends through the crankcase 10. The balanceshaft 115 and the crankshaft 123 are located at the union of the lowercrankcase 12 and the upper crankcase 13. To prevent oil from flowingfrom upper channel portion 113 and contacting the balance shaft 115, anoptional baffle assembly is located within the upper portion 113. Thebalance shaft 115 is provided to counteract the moment generated byrotation of the crankshaft 123, shown in FIG. 10. This arrangementproduces mass balancing of the first order. The balance shaft 115 andthe crankshaft 123 extend in a parallel relationship, as shown in FIG.10. The balance shaft 115 is rotatably mounted within a bore 1132 thatextends through the crankcase 10, as shown in FIGS. 9 and 10. Suitablebearing assemblies are provided for smooth rotation of the balance shaft115. The bearing assemblies are fixed using the fasteners describedabove. Preferably, the balance shaft 115 should be mounted in ananti-friction shell bearing but, alternatively, roller bearings can alsobe used. The balance shaft 115 is operatively connected by gear 1151 tothe crankshaft 123 through gear 1231. This connection is preferablylocated within the power take off assembly 50 on one end of thecrankcase 10.

[0098] The oil tank 11 forms a portion of a dry sump lubrication system.The lubrication system and the operation of the same will be describedin greater detail below.

[0099] As FIGS. 9 and 10 illustrate, the crankcase 10 includes at leastone crank chamber 121 and in the preferred embodiment includes oneisolated crank chamber for each engine cylinder. In accordance with thepresently disclosed embodiments of engines 1 and 2, three crank chambers121 are provided. Each crank chamber 121 includes an outlet opening Illconnected to the channel 112, described above. A bore 122 extendsthrough the crankcase 10 and each of the crank chambers 121, as shown inFIGS. 9 and 10. A crankshaft 123 is received therein, as shown in FIG.10. The crankshaft 123 can be a one-piece forging, cast or assembleddepending upon the engine application. For example, a cast crankshaftmay be used in low performance applications. The crankshaft 123 isrotatably mounted within a bore 122. Suitable bearing assemblies areprovided for smooth rotation of the crankshaft 123.

[0100] As shown in FIG. 25, a cylinder 124 extends through the crankcase10 above each of the crank chambers 121. In accordance with the presentinvention, the engines 1 and 2 each include three cylinders 124, asshown in FIG. 11. A piston 1241 is slidably received within the cylinder124. The piston 1241, shown in FIG. 11, reciprocates axially within thecylinder 124 as is known. The piston 1241 is connected to the crankshaft123 through a connecting rod 1242 and piston pin 1243 to convert axialmovement of the pistons 1241 to rotational movement of the crankshaft123 and vice-versa. A cooling passageway 125 extends around thecylinders 124, as shown in FIG. 25. The cooling passageway 125 isconnected to the engine cooling system 80 further described below. Asshown in FIG. 25, the cooling passageway 125 extends substantiallyaround the perimeter of the cylinders. This passageway has a generallyU-shaped configuration.

[0101] At present, the cylinder liners are formed with grey cast iron.The upper crankcase 13 is then cast around the liners. The uppercrankcase 13 may be formed from under-eutectic AlSi (e.g. cast-AlSi9)(with 9% silicon). The interior of the cylinder liners may then behoned. The use of grey cast iron increases the weight of the crankcase13. It is desirable to eliminate the use of the cylinder liners. Withthis in mind, it is contemplated that the cylinder liners may beeliminated. Instead, an interior surface of the upper crankcase 13 caninclude a thermal coating to reduce friction. This coating may beapplied plasma spraying or other suitable process. Alternatively,AlSi-alloys (alloys of aluminum and silicon) are used to form the linersfor the cylinders 124. The cylinder liners may be formed fromover-eutectic AlSi with primary silicon grains therein (e.g. AlSi19)(with 19% silicon) to minimize friction and wear. The crankcase 10may be formed from under-eutectic AlSi (e.g. cast-AlSi 9)(with 9%silicon). The cylinder liners are assembled to the cylinder block duringthe casting of the upper crankcase 13. Beforehand, a binding layerconsisting of eutectic AlSi 12 (with 12% silicon) is thermally sprayed(e.g. plasma sprayed) onto the outer wall of the liner to provide abetter bond and a better heat-removal property (high heat transfercoefficient) between the liner and the cylinder block 10. Alternatively,the cylinder liners can also be inserted into the cylinder block of theupper crankcase 13 mechanically with a force fit. It is alsocontemplated that the cylinder block 10 can be formed from over-eutecticAlSi (e.g. AlSi 19) without the need for separate cylinder liners. Withthis arrangement, however, the cylinder is more difficult to machine,more expensive and thus, is not presently preferred. In such aliner-less embodiment, the cylinders can be optionally provided with asurface coating for enhanced wear and friction properties. It iscontemplated that the pistons 1241 may be formed of aluminum coated withiron.

Cylinder Head Housing

[0102] The cylinder head housing 20 is secured to the upper end of thecrankcase, as shown in FIG. 8. The cylinder head housing 20 is bolted tothe crankcase and provides a combustion chamber 201 above each cylinder124. A pair of exhaust valves 21 and a pair of intake valves 22 aremounted in each combustion chamber 201. As shown in FIG. 11, the pair ofexhaust valves 21 are located on one side of the cylinder head housing20 and the pair of intake valves 22 are located on an opposite side ofthe cylinder head housing 20. The present invention, however, is notlimited to a pair of exhaust valves and a pair of intake valves; rather,a single exhaust valve and a single intake valve may be employed.Furthermore, more than two intake and exhaust valves may be provided.Furthermore, any combination of intake and exhaust valves iscontemplated provided each cylinder includes more intake valves thanexhaust valves.

[0103] As shown in FIG. 8, the intake valves 22 and the exhaust valves21 are disposed at an angle with respect to the vertical axis of theengine 1 or 2. This reduces the height of the cylinder head housing 20,which reduces the overall height of the engine 1 or 2.

[0104] The cylinder head housing 20 further includes at least oneexhaust passageway 23 for each combustion chamber 201 extending throughthe cylinder head housing 20, as shown in FIGS. 8, 12 and 13. Thepassageway 23 includes a pair of siamesed exhaust ports 231 that connectthe exhaust passageway 23 to the chamber 201, as shown in FIGS. 12 and13. Each of the pair of exhaust valves 21 is positioned in one of therespective exhaust ports 231 to selectively open and close the ports 231at predetermined intervals to permit the removal of exhaust gases fromthe chamber 201. An opposite end of the exhaust passageway 23 has anopening 232, as shown in FIG. 14, that is operatively connected to theexhaust manifold 30. The exhaust manifold 30 is secured to the cylinderhead housing 20 using suitable fasteners on a downwardly facing side ofthe cylinder head housing 20, as shown FIG. 5.

[0105] The cylinder head housing 20 further includes at least one intakepassageway 24 for each cylinder 124 extending through the cylinder headhousing 20, as shown in FIGS. 8, 12 and 13. The passageway 24 includes apair of siamesed intake ports 241 that connect the intake passageway 24to the chamber 201. Each of the pair of intake valves 22 is positionedin one of the intake ports 241 to selectively open and close theopenings 241 at predetermined intervals to permit the influx of fuel andair into the chamber 201. An opposite end of the intake passageway 24has an opening 242, as shown in FIG. 14, that is operatively connectedto the air intake and fuel injection system 40. The air intake and fuelinjection system 40 is secured to the cylinder head housing 20 oppositethe exhaust manifold 30 using suitable fasteners on an upwardly facingside of the cylinder head housing 20, as shown in FIG. 5. While theintake and exhaust ports are shown as being siamesed, they canalternatively remain separated until connected to the respective intakeand exhaust manifolds. The cylinder head housing 20 includes a sparkplug assembly 28 that is located in a central inclined position, asdescribed in greater detail below.

Valve Operating Assembly

[0106] A valve operating assembly illustrated in FIGS. 8 and 12-17operates the intake valves 22 and exhaust valves 21 in accordance withpredetermined engine operating parameters. The valve operating assemblyis located within the cylinder head housing 20 and is driven by thecrankshaft 123. As discussed in greater detail below in connection withthe power take off assembly 50, the crankshaft 123 extends from thecrankcase 10 into a power take off housing 59. A gear assembly 54 issecured to the crankshaft 123 within the power take off housing 59 andincludes a chain gear 542.

[0107] A cam shaft 29 is rotatably mounted within the cylinder headhousing 20. One end of the cam shaft 29 extends into a control chainchamber 202 within the cylinder head housing 20. The control chainchamber 202 extends into the cylinder block of the upper crankcase andenters the power take off assembly 50. A cam gear 293 is operativelycoupled to a chain gear 542 by a control chain 5, which extends aroundboth the gear 293 and gear 542. The control chain 55 extends through thecontrol chain chamber 202 into the power take off assembly 50. The camgear 293 and chain gear 542 are sized to have a 2 to 1 relationship.

[0108] The camshaft 29 is rotatably mounted to the cylinder head housing20 in a position between the intake and exhaust valves 21 and 22.Suitable bearing assemblies are provided for the smooth operation androtation of the camshaft 29 within the cylinder head housing 20. Asshown in FIG. 12, a plurality of cam lobes 291 and 292 are providedalong the camshaft 29 to operate the valves 21 and 22 in each cylinder.A cam lobe 291 provides the necessary motion to operate the intakevalves 22 through the rocker arm assembly 25. A pair of cams 292 providethe necessary motion to operate the exhaust valves 21 through the rockerarm assemblies 26. A cam 291 and a pair of cams 292 are positioned overeach cylinder, as shown in FIGS. 16 and 17. The cams 291 and 292 areoriented on the camshaft 29 to produce a predetermined timing foropening and closing the valves 21 and 22. The orientation of the cams291 and 292 vary for each cylinder such that all cylinders do notoperate at the same time, rather the cylinders operate in apredetermined sequence. While the camshaft 29 is illustrated with asolid construction, it is contemplated that the camshaft 29 may have ahollow construction. Furthermore, the camshaft may be forged, cast orassembled.

[0109] The valve operating assembly includes a Y-shaped intake rockerarm assembly 25 that operates both of the pair of intake valves 22, asshown in FIG. 13, in response to the cam lobe 291. The valve operatingassembly further includes a pair of exhaust rocker arm assemblies 26that operate the pair of exhaust valves 21, as shown in FIG. 13, inresponse to cam lobes 292. The intake rocker arm assembly 25 is a forkedassembly rocker arm having a pair of valve operating arms 251 and 252.One operating arm 251 operates one of the intake valves 22 and the otheroperating arm 252 operates the other intake valve 22. The fork likeshape of the rocker arm assembly 25 provides access to the spark plugassembly 27 positioned within the cylinder head housing 20. The sparkplug assembly 27 will be described in greater detail below. The forklike shape of the rocker arm assembly 25 reduces the overall width ofthe necessary assemblies to operate the valves for each cylinder.

[0110] In an effort to reduce the weight of the rocker arm assemblies 25and 26, the rocker arm assemblies 25 and 26 may be produced from analuminum alloy (AlSi) by forging or casting. The present invention,however, is not limited to rocker arm assemblies formed from aluminum;rather, it is contemplated that other materials including but notlimited to steel and alloys of the same may be cast or forged to formthe rocker arm assemblies 25 and 26.

[0111] The rocker arm assemblies 25 and 26 are rotatably mounted on arocker arm support axle 28 in a position between the intake and exhaustvalves 21 and 22. The stationary support axle 28 is mounted to thecylinder head by a plurality of fastener assemblies 281, as shown inFIGS. 16 and 17. The fastener assemblies 281 may include screw typefasteners, pin fasteners or other similar fastener assemblies forsecuring the support axle 28 within the cylinder head housing 20 andpreventing its rotation. The rocker arm support shaft 28 is mounted tothe cylinder head housing 20. The axle 28 is laterally offset andvertically spaced from the camshaft 29, as shown in FIGS. 12, 14 and 18.This arrangement results in a compact construction that reduces theoverall height of the cylinder head housing 20. It is contemplated thatthe axle 28 may be located on the vertical axis of the cylinder oradjacent to the same.

[0112] The camshaft 29 is operatively connected to the crankshaft 123,as described below. The cam gear associated with the crankshaft gear aresized to have a 2 to 1 relationship. The angled intake and exhaustvalves 21 and 22 provide an enlarged area within the cylinder headhousing 20 between the valves in which to locate the cam shaft, axle andthe rocker arm assemblies 25 and 26. This also provides sufficient spaceto maintain the 2 to 1 relationship between the cam gear and thecrankshaft gear without increasing the height of the cylinder headhousing 20.

[0113] The rocker arm assembly 25 will now be described in greaterdetail, reference being made to FIGS. 12 and 14. As described above, therocker arm assembly 25 has a pair of operating arms 251 and 252. A freeend of each of the pair of operating arms 251 and 252 is positioned overa respective intake valve 22 and includes an hydraulic adjuster 253 forcontacting the intake valve 22. The hydraulic adjuster 253 abuts theupper surface of the valve stem of the intake valve 22. The hydraulicadjuster 253 is located within a cavity 2511 and 261 in the respectivearm 251 and 252. A passageways 2512 and 262 extend from the cavities2511 and 262, respectively, to the rocker arm support axle 28. Thepassageways 2512 and 262 are hydraulically linked to the rocker armsupportaxle 28. The rocker arm support axle 28 includes a centralpassageway through which a supply of hydraulic fluid (preferablylubricant from the lubricant system) or other suitable lubricant flows.The fluid passes from the central passageway through radial openings 282to the passageways 2512 and 262. The fluid flows through the passageways2512 and 262 to the cavities 2511 and 261 where it biases the hydraulicadjuster 253 into contact with the intake valve 22. The fluid insuresthat the hydraulic adjuster 253 is always in contact with the intakevalve 22 such that zero lash exists between the valve and hydraulicadjuster 253. This insures that the entire motion of the cam 291 istransferred to the intake valves 22 to facilitate their opening andclosing. Although fluid is used to bias the hydraulic adjuster 253 intoengagement with the valves 22 in the embodiment illustrated, it iscontemplated that a screw adjuster assembly or other mechanical assemblycan be provided to perform the same operation.

[0114] An opposite end of the rocker arm assembly 25 includes a camfollower 254. The follower 254 may include a roller assembly havingbearings that is rotatably mounted to the rocker arm assembly 25. Thefollower 254 travels along the cam 291, which causes the rocker armassembly 25 to pivot about the rocker support axle 28. The motion of thecam 291 is transferred to open and close the intake valves 22. Fluidfrom the central passageway 281 may be directed through anotherpassageway, not shown, in the rocker arm assembly 25 to provide a supplyof fluid to lubricate the follower assembly 254 to provide for smoothoperation. The present invention, however, is not limited to the rollerfollowers described herein; rather, it is contemplated that otherfollowers including but not limited to sliding blocks may be utilized tofollow the cam 291.

[0115] The rocker arm assembly 25 has a compact angled construction, asshown in FIG. 14 so as to allow for a narrow and low construction.Similarly, the low arrangement of the camshaft 29 and associated drivechain wheel, which also does not project beyond the cylinder headhousing 20, as seen in FIGS. 16 and 17 assists in constructing an enginewith a narrow and low profile.

[0116] As seen in FIGS. 8, 12 and 14, the camshaft 29 and the supportaxle 28 are offset relative to the longitudinal axis of the cylinder.The camshaft 29 is offset to provide room for the spark plug assembly27, described below. Both the camshaft 29 and the support axle 28 arelocated closer to the exhaust valves 21 than the intake valves 22. Theoffset nature of the support axle 28 increases the overall length of theintake rocker arm assembly 25. This increases the lever arm of theintake rocker arm assembly 25 and maximizes the force (within the sizeconstraints of the cylinder head housing 20) applied to operate bothintake valves 22 with one rocker arm assembly. The intake and exhaustvalves are disposed at an angle with respect to the cylinder axis. Inprinciple, however, also other geometries (e.g. with a centralarrangement of the camshaft 29) are conceivable. Alternatively, therocker arm support axle 28 may be located closer towards the intakevalves so as to make the forked operating arms 251 and 252—which areheavy due to this construction—shorter and thus less heavy. With thisarrangement, the location of the camshaft 29 should also be relocated tomaintain the lever arm of the intake rocker arm assembly 25.

[0117] The rocker arm assemblies 26 will now be described in greaterdetail. Each exhaust rocker arm assembly 26 has the same construction. Afree end of the rocker assembly 26 is positioned over a respectiveexhaust valve 21 and includes a hydraulic adjuster 263 for contactingthe exhaust valve 21. The hydraulic adjuster abuts the upper surface ofthe valve stem of the exhaust valve 21. Like the hydraulic adjuster 253,the hydraulic adjuster 263 is located within a cavity 261. A passageway262 extends from the cavity 261 to the rocker arm support axle 28. Thepassageway 262 is hydraulically linked to the rocker arm support axle 28through radial openings 282. The fluid flows through the passageway 262to the cavity 261 where it biases the operating assembly 263 intocontact with the exhaust valve 21. The fluid ensures that the hydraulicadjuster 263 is always in contact with the exhaust valve 21 such thatzero lash exists between the valve and hydraulic adjuster 263. Thisinsures that all motion of the cam 292 is transferred to the exhaustvalve 21 to facilitate opening and closing. Although fluid is used tobias the hydraulic adjuster 263 into engagement with the valve 21, it iscontemplated that a mechanical assembly (e.g. a screw adjuster) may beprovided to perform the same operation.

[0118] An opposite end of the exhaust rocker arm assembly 26 includes acam follower 264. The follower 264 has a similar construction to thefollower assembly 254, described above. The rocker arm assembly 26 alsohas a compact angled construction, as shown in FIG. 14 so as to allowfor a narrow and low construction.

[0119] The construction of the hydraulic adjusters 253 and 263 will nowbe described in greater detail in connection with FIG. 15. The hydraulicadjusters 253 and 263 have the same construction. The hydraulic valveadjusters 253 and 263 are maintenance free and require no adjustment.The hydraulic adjuster 263 is positioned within the cavity 261. Thehydraulic adjuster 263 includes an inner stationary piston 2631 and anouter movable piston 2632, which is located between the cavity 261 andthe inner stationary piston 2631. The inner stationary piston 2631includes a central cavity 2633 that is in communication with the cavity261, as shown in FIG. 15.

[0120] An opposite end of the piston 2631 includes an aperture 2634 suchthat the cavity 2633 is in fluidic communication with a cavity 2635 inthe piston 2632. A ball and seat check valve 2636 selectively closes theaperture 2634. A valve contacting cap 2637 is pivotably mounted on anend of the piston 2632. The cap 2637 contacts the valve stem of theexhaust valve 22 when the piston 2632 is in an extended position, asshown in the right side of FIG. 15.

[0121] In operation, hydraulic fluid flows through channel 262 into thecavity 261. After the cavities 261 and 2633 have filled with fluid, thevalve 2636 opens to permit the flow of fluid into cavity 2635 throughaperture 2634. As the cavity 2635 fills with hydraulic fluid, the piston2632 extends to the position shown in the right side of FIG. 15. Thespring assembly 2638 is located in the cavity 2635. The downward travelof the piston 2632 is limited by contact with the valve stem and a seal2639 that is secured to one end of the piston 2632 and is slidablyreceived around the piston 2631. When in the normal downward steadystate position, the contacting cap 2637 contacts the valve stem suchthat motion of the rocker arm assembly is transferred to the valve toopen the valve at predetermined locations of the camshaft 29. Afterengine shut off, a sufficient amount of fluid is maintained in thecavity 2635 to maintain the outer movable piston 2632 in engagement withthe corresponding valve stem.

[0122]FIGS. 16 and 17 illustrate an axial section through the camshaft29 and the rocker arm support axle 28. The camshaft 29 is mounted in abearing bracket 293 with two collars 294 and 295. Lubricant is suppliedto the clearance region between these two collars 294 and 295. By meansof this double plain bearing in the respective bearing bracket 293, thebearing becomes very rigid and the dynamic changing loads occurringduring operation can be accommodated efficiently. Mounting of thecamshaft 29 is effected by inserting it in from one end of the cylinderhead housing 20 near the power take off end of the engine. The camshaft29 is secured by a plate positioned within the cylinder head housing 20against axial shifting. The plate extends through a vertical slotlocated within the cylinder head housing 20. The plate may be furtherused to orient the axle 28 within the cylinder head housing 20. It isalso contemplated that a pin may be used to secure the camshaft againstaxial shifting. The pin may be located in a slot or groove extendingaround the perimeter of the camshaft.

[0123] Although the operation of the intake valves 22 and exhaust valves21 has been described in connection with rocker arm assemblies 25 and26, other assemblies are contemplated for operating the valves. Forexample, the valves may be electromagnetically operated. Alternatively,the valves may be hydraulically operated using a slave piston/masterpiston arrangement. Furthermore, the Y-shaped rocker may be used toactuate the exhaust valves. Individual rocker arms may be used tooperate intake valves. With this arrangement, the location of the sparkplug assembly 27 must be relocated. It is also contemplated that gassprings may be used to bias the valves into a closed position when highrotation speeds are desired for high rpm output. It is also contemplatedthat a variable valve train may be substituted to vary the timing of thevalve operation.

Spark Plug Assembly

[0124] The spark plug assembly 27 will now be described in greaterdetail in connection with FIG. 18. A spark plug 271 is connected bythreaded engagement to the cylinder head housing 20, as shown in FIG. 18such that an electrode portion of the spark plug 271 extends into thecylinder. The spark plug assembly 27 is located between the intakevalves 22 and the exhaust valves 21 closer to the intake valves 21because the intake side of the engine is cooler than the exhaust side ofthe engine. It is desirable to isolate the spark plug 271 from theremainder of the cylinder head housing 20, which contains oil therein. Atube assembly 272 surrounds the spark plug 271. The tube assembly 272 ispreferably formed from a die cast plastic. It, however, is contemplatedthat other light weight materials may be used to form the tube assembly272 so long as the tube assembly 272 isolates the spark plug 271 fromthe oil-carrying portions of the cylinder head housing 20. It ispreferable that the spark plug assembly 27 be inclined at an angle withrespect to the central axis of the cylinder. The angle between the sparkplug assembly and the intake valves is small (e.g. 3° is preferable).The angle, however, may be zero.

[0125] Each tube assembly 272 is sealingly inserted into a pedestal 273on the cylinder head housing 20, which forms a socket for the spark plug271. A slight compression fit between the tube 272 and a bore in thepedestal 273 can provide a sealing engagement between the two componentsalthough this sealing engagement can also be augmented by providing ano-ring between the two compartments. On an outer end, a seal 274 isvulcanized onto the tube assembly 272 which effects the sealing betweenthe tube assembly 272 and a cylinder head cover 275. Alternatively, theseal 274 can be provided as a separate component between the tube 272and cover 275. Use of the tube 272 provides for a lighter weight headassembly and also simplifies the casting of the cylinder head since theisolating tube is not cast as part of the cylinder head. The tubeassembly 272 accommodates a plastic body spark plug connector 276 inwhich the ignition coil or the spark transformer are cast. In this way,the path of the high voltage to the spark plug 271 can be kept extremelyshort. From the outside, only a low voltage is supplied to the plasticbody spark plug connector 276 and the ignition coil contained therein.The plastic body spark plug connector 276 and the spark plug 271 caneasily be removed through the tube assembly 272. The plastic body sparkplug connector 276 abuts the inner side of the tube assembly 272. Aventing assembly is provided to enable venting from the spark plugregion towards the environment. A splash water screen 2763 is attachedto the plastic body 276.

[0126] A cylinder head cover 275 is attached to the cylinder headhousing 20 using a plurality of fastener elements 2571, as shown in FIG.19. The cylinder head cover 275 is preferably formed from aluminum orsome synthetic material. The connection between the cylinder headhousing 20 and the cylinder head cover 275 is acoustically decoupled. Anelastomeric gasket 2753 is positioned between the cylinder head housing20 and the cylinder head cover 275 to provide a seal between the twocomponents. The gasket 2753 has a protruding portion 2754 that isconfigured to sealingly engage a slot 2755 in the cylinder head cover275. This engagement maintains the gasket in a desired position betweenthe cylinder head housing 20 and the cylinder head cover 275 and helpsprevent the gasket 2753 from dislocating and causing leaks. In addition,the elastomeric gasket also reduces and prevents a direct soundpropagation from the cylinder head housing 20 to the cylinder head cover275 thereby reducing overall noise emanating from the engine. A furtherelastomeric gasket 2752 is provided between the fastener element 2751and cylinder head cover 275 to seal the connection therebetween and alsoblock direct sound propagation from the cylinder head housing 20 to thecylinder head cover 275 through the fastener 2751. With thisarrangement, the cylinder head cover 225 is isolated from the cylinderhead housing 20.

Exhaust Manifold

[0127] A preferred embodiment of the exhaust manifold 30 will now bedescribed in connection with FIGS. 21-24. The exhaust manifold 30includes a first manifold 31 and a second manifold 32, as shown in FIG.24. The first manifold 31 is connected to one side of the cylinder headhousing 20. It is preferably located on the smaller downward facing sideof the cylinder head housing 20 because it does not require as muchspace as the induction system 40, described below. The first manifold 31includes at least one exhaust passageway 311 that is operatively coupledto each exhaust passageway 23 in the cylinder head housing 20. Eachexhaust passageway 311 connects to a main exhaust passageway 312, whichextends in a direction towards the power take off assembly 50. With thisarrangement, exhaust gases exit the cylinder head housing 20 througheach exhaust passageway 23 when the respective exhaust valves 21 areopened. The exhaust gases then travel through the exhaust passageway 311to the main exhaust passageway 312.

[0128] The first manifold 31 is connected at the end nearest the powertake off assembly 50 to the second manifold 32. The second manifold 32includes a main exhaust passageway 321. The exhaust gases travel throughthe main exhaust passageway 321 into the muffler system 33.

[0129] Due to US Government regulation, it is necessary to cool theexhaust components to limit the temperature of these components below athreshold value. It is desirable to cool the exhaust gases as the gasespass through the exhaust manifold 30 and an associated muffler system33. The muffler system 33 preferably includes a first muffler 331directly connected to the exhaust manifold 30 and a second muffler 332connected to the first muffler 331.

[0130] The first and second manifolds 31 and 32 are equipped with anopen loop cooling system for cooling the manifolds 31 and 32 and theexhaust gases contained therein. Each manifold 31 and 32 has a doublejacket construction that permits cooling water to flow around theinterior of the manifolds 31 and 32 without mixing with the exhaustgases. The first manifold 31 is preferably cast. The second manifold 32is preferably formed from stainless steel.

[0131] The first manifold 31 has an inner manifold 313 and an outermanifold 314, as shown in FIGS. 22 and 23. The spacing between the innerand outer manifolds 312 and 314 forms a cooling passageway 315. Theinner and outer manifolds 313 and 314 are interconnected at variouspoints along the manifold. The cooling passageway 315 has a generallyu-shaped configuration when viewed from a vertical cross section suchthat it surrounds the main passageway 311 on the top, bottom and atleast one side. The cooling water enters the passageway 315 through atleast one inlet 316. The cooling water then travels through the coolingpassageway 315 and exits through at least one outlet 317.

[0132] The second manifold 32, as shown in FIG. 24, also has an innermanifold 322 and an outer manifold 323. The spacing between the innerand outer manifolds 322 and 323 forms a cooling passageway 324,therebetween. The cooling passageway 324 substantially surrounds themain exhaust passageway 321. The cooling water enters the coolingpassageway 324 through at least one inlet 325 located near theconnection between the first manifold 31 and the second manifold 32. Thecooling water exits the cooling passageway through at least one outlet326 located near the point where the second manifold 32 enters the firstmuffler 331.

[0133] The cooling system for the exhaust manifold 30 and muffler system33 is an open loop cooling system. Cooling water is supplied to thefirst and second manifolds 31 and 32 by a jet pump of the propulsionunit of the personal watercraft 5, which draws cooling water from thebody of water in which the personal watercraft 5 is operating. An openloop cooling system can be used for the exhaust manifold 30 because thegeometry of the cooling jacket for the exhaust manifold 30 is relativelysimple with larger passageways. There is less concern for the cloggingof these passageways. On the contrary, the geometry of the coolingsystem for the cylinder head housing 20 and crankcase 10 is more complexwith smaller passageways. There is a greater concern about clogging thatmay occur when using a coolant drawn from outside the watercraft 5. Assuch, a closed loop cooling system is preferred for the cylinder headhousing 20 and crankcase 10.

[0134] The cooling passageways 315 and 324 sufficiently cool themanifolds 31 and 32. The temperature of the exhaust gases, however,remains too high. It must be further cooled before venting to theatmosphere or released into the water. It is desirable to cool theexhaust gases as the exhaust gases enter the first muffler 331. At leastone injection nozzle 34 is located adjacent the end of the main exhaustpassageway 321, such that a stream of cooling water is injected into theexhaust stream as the exhaust stream enters the first muffler 331.Although it is preferable that the at least one injection nozzle 34 belocated within the muffler 331, it is contemplated that the injectionnozzles 34 may be located within the main exhaust passageway 323.

[0135] It is possible for the personal watercraft 5 to overturn orrollover during operation. It is desirable to prevent the cooling waterused to cool the exhaust gases from traveling within the main exhaustpassageways 314 and 323 to the cylinder head housing 20. The design ofthe second manifold 32 and the connection between the second manifold 32and the first muffler 331 prevent the return of the cooling water to thecylinder head housing 20.

[0136] The second manifold 32 terminates within the first muffler 331 ata central location. The outlet opening for the main exhaust passageway323 is spaced from the top, bottom and side walls of the first muffler331. With this arrangement, cooling water that has accumulated withinthe first muffler 331 should not enter the main exhaust passageway 323because the cooling water should travel along the sides of the firstmuffler 331 (spaced from the outlet) when rollover occurs.

[0137] In the event that some cooling water enters the main exhaustpassageway 323, the configuration of the second manifold 32 preventspassage of cooling water to the cylinder head housing 20. The secondmanifold 32 contains a unshaped bend or gooseneck portion that traps thecooling water. With this arrangement in a rollover condition, thecooling water must first travel downward from the first muffler 331through the bend or gooseneck portion and then upward before enteringthe first manifold 31. The change in direction of the main exhaustpassageway 323 in the gooseneck portion essentially prevents any coolingwater from entering the first manifold 31 or the cylinder head 32.

[0138] The present invention is not limited to the above-describedgooseneck portion for preventing water from entering the first manifold31 at the cylinder head 20; rather, other geometries that produce asimilar effect are considered to be well within the scope of the presentinvention.

[0139] An alternative embodiment of the exhaust manifold will now bedescribed in connection with FIGS. 43 and 44. The exhaust manifold 300is connected to one side of the cylinder head housing 20. Like themanifold 30 described above, the manifold 300 is preferably located onthe smaller downward facing side of the cylinder head housing 20. Theexhaust manifold 300 includes at least one exhaust passageway 310 thatis operatively coupled to each exhaust passageway 23 in the cylinderhead housing 20. Each exhaust passageway 310 connects to a main exhaustpassageway 320. The exhaust gases exit the cylinder head housing 20through each exhaust passageway 23 when the respective exhaust valves 21are opened. The exhaust gases then travel through the exhaust passageway310 to the main exhaust passageway 320. The main exhaust passageway 320first directs the exhaust gases toward the front of the personalwatercraft, then in an opposite direction through knee bend 330 towardthe rear of the personal watercraft. The exhaust gases may then exit theexhaust manifold 300 to a muffler system and/or water trap. The mufflersystem may include a pair of mufflers.

[0140] In this alternative arrangement, the exhaust manifold 300 alsohas a double jacket construction that permits cooling water to flowaround the exhaust gases without mixing the cooling water and theexhaust gases. The double jacket construction includes an inner manifold340 and an outer manifold 350, which create a cooling chamber 370therebetween. Webs 360 separate the cooling chamber 370 into a firstportion 3701 and a second portion 3702, as shown in FIG. 22. The coolingwater passes through the cooling chambers 3701 and 3702, as shown inFIG. 44.

[0141] Like the manifold 30 the exhaust manifold cooling system is anopen loop cooling system. As such, a jet pump of the propulsion unitdraws cooling water from the body of water in which the personalwatercraft 5 is operating, shown in FIG. 44. The cooling water issupplied to the exhaust manifold 300 through a primary inlet port 3510located in the bend 330 of the exhaust manifold 300, as shown in FIG.43. The cooling water then flows through the first chamber portion 3701until it connects with the second chamber 3702 at the rear portion ofthe exhaust manifold 300. The cooling water then flows back through thesecond chamber 3702 until it is discharged through the outlet port 3520back into the body of water. Thus, the separation of the chamber 370into two portions 3701 and 3702 that are interconnected only at an endof the exhaust manifold distant from the cooling intake and outlet portsprovides for a U-shaped cooling circuit in the manifold, enhancing thecooling efficiency of the manifold.

[0142] These cooling arrangement maintain the exhaust manifolds 30 and300 at a lower temperature than the cylinder head housing 20 and thecylinder block 10. As a result, the exhaust manifolds 30 and 300function as a heat sink, withdrawing heat from the cylinder head housing20 and the cylinder block 10. This reduces the cooling requirementsplaced on the closed loop cooling system 80, described below. Thecoolant in the exhaust manifold (e.g. the water drawn from the body ofwater) has a lower temperature than the coolant for the closed loopcooling system, described below.

[0143] At least one temperature sensor 39 is located in the muffler tomeasure the temperature of the exhaust gases. The exhaust manifold 300is equipped with an injection cooling system, which supplies additionalcooling water to the exhaust manifold. A first injection nozzle 381sprays cooling water directly into the exhaust passageway 320 in adirection away from the cylinder head housing 20. A second injectionnozzle 383 sprays cooling water directly into the exhaust passageway 320also in a direction away from the cylinder head housing 20. The locationof the nozzles in the knee of the exhaust manifold prevents the backwardtravel of the cooling water into the cylinder head. The combined openloop cooling system with the injection cooling system functions to coolboth the exhaust manifold and the exhaust gases within the manifold.

Air Intake and Fuel Injection System

[0144] The air intake and fuel injection system or induction system 40will now be described in connection with FIGS. 26-31. The system 40 isconnected to the cylinder head housing 20 opposite the exhaust manifold30. The air intake into the engine 1 or 2 is effected from within thehull of the personal watercraft 5 via an air box, not shown, butdisclosed in US Provisional Patent application No. 60/224,355, filed onAug. 11, 2000, entitled “WATERCRAFT HAVING AIR/WATER SEPARATING DEVICE”and U.S. Provisional Patent Application No. 60/229,340, filed on Sep. 1,2000, entitled “PERSONAL WATERCRAFT HAVING IMPROVED FUEL, LUBRICATIONAND AIR INTAKE SYSTEMS” the specifications of which are incorporatedspecifically herein by reference. The air box comprises an air inlet inthe form of a snorkel, a water separator unit and a muffler unit. Theair box is located apart from the engine and connected to the engine viaa tube or hose to prevent water from entering the air intake system.

[0145] The air flows through the tube connecting the air box with theengine, and then passes to an air intake manifold or plenum 41,illustrated in FIGS. 26-31. The air manifold 41 is preferably formedfrom a plastic material. The present invention, however, is not limitedto the use of a plastic material; rather, metals, high strength alloysand other suitable synthetic materials may be used. The end cap 413 maybe formed integrally with the air manifold.

[0146] The air manifold 41 has a symmetrical geometry. With thisarrangement, air flow into the air manifold 41 can be provided at eitherend of the air manifold 41, thereby enabling use of the same airmanifold 41 in either a normally aspirated engine 1 or a superchargedengine 2, which engines have different flow paths for air into the airintake manifold. In the normally aspirated engine, the air from athrottle (if the engine has fuel injection) or a carburetor (if theengine does not have fuel injection) flows into one end of the airmanifold 41, as shown for example in FIG. 4. Preferably, this end facesthe airbox to shorten the distance and the pressure loss between theintake manifold and the airbox.

[0147] Irrespective of which end of the air manifold is used to intakeair, in a fuel injection version of the engine, the air manifold 41includes a throttle body 411 containing a throttle at the plenum inletto regulate the flow of air into the manifold 41. The degree of openingof the throttle of the throttle body 411 is controlled by the enginemanagement system 200. The throttle body 411 further includes a by-passidle valve 4111. The by-pass idle valve 4111 is preferably controlled bya stepper motor that controls the cross sectional opening of the by-passidle valve 4111 and the amount of air flowing through it. Alternatively,it is contemplated that the idle valve 4111 may include anelectromagnetically operated valve. The operation of the by-pass idlevalve 4111 is controlled by the engine management system 200. The enginemanagement system operates the stepper motor based on the engine speedto adjust it to a given threshold value. In normal operation, the idlevalve 4111 is open when the throttle of the throttle body 411 is closed.This permits the flow of a predetermined amount of air into the manifold41 during an engine idling less than the normal air intake into the airmanifold 41. The idle valve 4111 is not fully closed when the throttleof the throttle body 411 is open. In a normal full load steady stateoperating condition, the idle valve 4111 is partly but not entirelyopen. This provides a reserve of intake air used for transient engineoperating conditions (e.g., a rapid deceleration phase). The steppermotor is operated such that the maximum amount of air can be drawn intothe air manifold 41 so that the air/fuel mixture is not too high. Thelocation of the throttle body 411 is different for the normallyaspirated engine 1 and the supercharged engine 2. It is contemplatedthat the throttle body 411 may be replaced by a carbureter in a non-fuelinjected version of the engine.

[0148] The air manifold 41 further includes at least one swing pipe 412for each cylinder. Each swing pipe 412 is operatively connected to therespective intake passageway 24 to supply air to the combustion chambersthrough intake openings 241. The flow pattern of the air within the airmanifold 41 is indicated by the arrows in FIGS. 27-29 and 31. As shown,the air enters the air manifold 41 via the throttle body 411. The airpasses radially through a cylindrical flame arrester 42 and then flowsthrough each swing pipe 412 to the respective intake passageway 24.

[0149] The flame arrester 42 in the air manifold 41 prevents backfire offlames from entering the engine compartment interior within the hull ofthe personal watercraft. The flame arrester 42 includes a perforatedinner pipe 421 and a pleated porous outer shell 422. In accordance withthe present invention, the location of the flame arrester 42 isadvantageous. The flame arrester 42 is located within the centralpassageway in the air manifold 41. As such, the flame arrester 42 islocated between the swing pipe 412 and the air inlet. In the event of abackfire, this location is advantageous because all flames are caught bythe flame arrester 42 before passage to the air inlet (i.e., thethrottle or the supercharger). Thus, backfire flame cannot reach outsideof the engine, especially important when the engine is installed on awatercraft or aircraft where an engine compartment fire can be moredisastrous than in an automobile. Although a cylindrical flame arrester42 is illustrated, it is also contemplated that the flame arrester maybe in the form of a flat plate or an arcuate member.

[0150] The air manifold 41 is constructed to withstand the build up ofback pressure in the event of a backfire. The manifold 41 is configuredsuch that the back pressure is dissipated within the swing pipe 412. Toprevent failure or cracking of the manifold in the event of asignificant build up of back pressure, a pressure relief valve may beprovided. The pressure relief valve may be made integral with an end cap413, which is secured to an end of the air manifold 41, as shown in FIG.27.

[0151] In the supercharger version of the engine 2, the supercharger 90and the throttle body 411 are interconnected between the air box and theair manifold 41. The throttle body 411 is located between the airmanifold 41 and the supercharger 90. The supercharger assembly 90,however, is connected to an opposite end of the air manifold 41, asshown in FIGS. 30 and 31. The location of the throttle body 411 is alsorelocated to this end. As such, the air manifold 41 is designed suchthat the throttle body 411 and the pressure relief valve, if provided,can be located on either end of the manifold 41 to provide increasedflexibility such that the same manifold geometry can be used for eitherthe supercharger version or the normally aspirated version of theengine.

[0152] The intake manifold 41 also includes at least one drainage port.The drainage plug is removably located within the drainage port. In theevent that water enters the interior of the intake manifold 41, theplugs can be removed to drain the water. Alternatively, a hose can beconnected to the drainage port having a valve at an opposite end formore controlled drainage. Furthermore, it is contemplated that anautomatically operated drainage valve may be provided to drain the airmanifold upon engine shutdown.

[0153] It is contemplated that the air manifold 41 may include a coolingjacket 49 along an exterior wall of the air manifold 41, as shown inFIG. 29. The cooling jacket 49 cools the air within the air manifold 41and, more particularly, the swing pipe 412 before entering thecombustion chambers. The cooling of the intake air is especially usefulfor a supercharge version of the engine because the operation of thesupercharger (by compressing) the air increases the temperature of theair. The cooling jacket may be linked to the open loop cooling system.

[0154] The air intake and fuel injection system 40 further includes afuel injection assembly 43. The fuel injection assembly 43 includes acommon fuel rail 431. The fuel rail 431 extends along an upper portionof the intake manifold 41, as shown in FIGS. 26, 27, 30 and 31. It ispreferred that the pressure of the fuel into the fuel rail 431 beregulated by the fuel supply assembly 203 located in the fuel tank 204.In an arrangement where the fuel supply is not controlled in the fueltank, an optional pressure control valve 432 is located at one end ofthe fuel rail 431. The pressure control valve 432 is provided to controlfuel pressure within the fuel injection assembly 43. In thisarrangement, a separate fuel return line is required.

[0155] At least one fuel injection nozzle 434 extends from the fuel rail431 to the each swing pipe 412 adjacent the connection to each intakepassageway 24. A fuel injection nozzle 434 is provided for each enginecylinder. The swing pipe 412 extends along the sides of the fuelinjection nozzle 434. This increases air flow around the injectionnozzle 434 such that no pockets of reduced air flow are producedadjacent the nozzle 434 because reduced air flow may produce residue onthe wall of the swing pipe adjacent the nozzle, which could reduceperformance and flow of fuel into the cylinder chamber. Additionally, toprevent the formation of pockets, the nozzles 434 may extend into theswing pipe 412. Fuel from the injection nozzle 434 is mixed with the airwithin the swing pipe 412 as the air enters the intake passageway 24.The fuel injection nozzles 434 are electromagnetically controlled by theengine management system 200 so that the nozzles 434 are independentlyand sequentially operated.

Power Take Off Assembly

[0156] The power take off assembly 50 of the engine 1 or 2 will now bedescribed in connection with FIGS. 32-34 and 36. The crankshaft 123,described above, extends from one end of the crankcase 10, as shown inFIG. 33. The rotation motion of the crankshaft 123 is transferred to adrive shaft 51. A threaded connecting assembly 52 is secured to the endof the crankshaft 123. The threaded connecting assembly 52 includes aplurality of teeth 521 that extend around an inner periphery of one endof the connecting assembly 52. The teeth 521 are adapted to mate withcomplementary teeth 511 on the drive shaft 51. As shown in FIGS. 36 and37, the teeth 511 have a generally arcuate shape. Although a generallylinear tooth arrangement is considered to be well within the scope ofthe present invention, the arcuate tooth is preferred. The arcuatearrangement allows for slight angular deviations between the crankshaft123 and the drive shaft 51. This is especially important when thecrankshaft 123 and the drive shaft 1 are not in exact alignment or whenthe personal watercraft is operated in extreme conditions, such as, forexample, when jumping waves. The use of the threaded connecting assembly52 is also advantageous. In the event of wear resulting from non-exactalignment, only the connecting assembly 52 need be replaced.

[0157] The arcuate teeth 511 of the connecting assembly 52 arelubricated with engine oil. The oil is supplied from a first crankshaftmain bearing 1232 via hollow bores 1233 in the crankshaft 123. The oilthen flows to the arcuate teeth 511. This arrangement reduces enginemaintenance because the operator no longer needs to grease theconnection between the crankshaft and the drive shaft. The lubricationis performed by the lubrication system of the engine. The power take offhousing 59 seals the components contained therein with the power takeoff assembly 50. Thus, protecting these components from exposure tomarine conditions.

[0158] The connecting assembly 52 includes a sealing extension 522,wherein the extension 522 extends along a portion of the drive shaft 51.An o-ring seal 523 or other suitable sealing member is positionedbetween the sealing extension 522 of the connecting assembly 52 and thedrive shaft 51. There is no relative rotational movement between thedrive shaft 51 and the connecting assembly 52. As such, there are norotational stresses on the o-ring seal 523. The sealing extension 522and the o-ring 523 prevents lubricant from escaping from the engine. Alabyrinth sealing arrangement may be provided between the sealingextension 522 and the power take off housing 59 to prevent the passageof lubricant from the power take off assembly 50 around the drive shaft51. Alternatively, a screw or worm conveyor may be provided, whichconveys lubricant back to the power take off assembly. At least one boremay be provided to form a shortcut such that the oil is drawn into thescrew conveyor.

[0159] Additionally, the sealing of the drive shaft 51 with respect tothe outside is effected by a sealing assembly 53. The sealing assembly53 includes several sealing elements that can be used alone or incombination. The sealing assembly 53 includes flexible bellows 531, ashaft seal ring 532, and sealing rings 533. The flexible bellows 531connects the power take off housing 59 with an external bearing carrierrace 5311, which in turn is rotatably mounted on the drive shaft 51 viatwo self lubricating antifriction bearings (rolling bearings) 5312 and abearing carrier inner race 5313. Sealing between the two bearing carrierraces 5311 and 5313 is effected by the shaft sealing ring 532. Thesealing rings 533 (in the form of polymeric o-rings) act as a sealbetween the bearing carrier inner race 5313 and the drive shaft 51. Thesealing rings 533 also ensure a reliable fit between the two parts. Asafety ring or clip 534 secures the bearing carrier inner race 5313 onthe drive shaft 51 against any axial displacement. This may also beaccomplished using a step formed in the drive shaft 51. The flexiblebellow 531 is clamped to the power take off housing 59 and the externalbearing carrier race 5311 by clamps 5314 and 5315, respectively.

[0160] Alternatively, the antifriction bearings 5312 are lubricated withengine oil. The oil is supplied from a first crankshaft main bearing1232 via hollow bores 1233 in the crankshaft 123. The oil flows throughthe arcuate teeth 511 to the antifriction bearings 5312 and finallyreturns between the power take off housing 59 and the connectingassembly 52 into the interior of the engine. With this arrangement, asecond flexible seal is provided in the event the flexible bellow 531fails.

[0161] The power take off assembly 50 further includes a gear assembly54, as shown in FIGS. 36 and 37. The gear assembly 54 includes a maingear 541 secured to the crankshaft 123 for driving the balance shaft115, a chain gear 542 integrally connected to the main gear 541 fordriving a cam control chain 55, and a large gear 543. It is contemplatedthat the chain gear 542 may be a separate component that is either forcefit, fastened to or integrated into the crankshaft 123. The large gear543 includes at least a first gear 5432 for engagement with a starter 56through intermediate gear 561, as shown in FIG. 37 A second gear 5431may be secured to the large gear 543 if the engine 2 is so equipped fordriving a supercharger 90, as described below and shown in FIG. 38 Forreducing the number of required parts for the engine family, a singlegear 543 having both gears 5431 and 5432 may be used in either the blownor normally aspirated engines. It is also contemplated that the largegear 543 is formed as a single gear such that a portion of each tooth ofthe gear is used to drive the supercharger and another portion is usedto drive the starter.

[0162] Linking the intermediate gear 561 for the starter assembly 56 tothe crankshaft 123 through the gear 543 results in a reduction of theengine profile. A thrust screw drive within the intermediate gear 561for the starter assembly 56 allows for an automatic engagement of adrive pinion 562 with the first gear 5432 during the starting procedure.The intermediate gear 561 moves the drive pinion 562 into engagementwith the first gear 5432 against the bias of a return spring 563. Atleast one dampening spring 564 is provided to absorb vibration. Afterthe starters operation is complete, the thrust screw drive disengagessuch that the return spring 563 biases the drive pinion 562 out ofengagement with the first gear 5432. The drive pinion 562 is mounted toa pinion shaft 565 that is connected to the starter assembly 56 suchthat rotational movement generated by the starter assembly 56 istransferred to the drive pinion 562. The pinion shaft 565 is slidablyand rotatably received within a recess in the power take off housing 59.

[0163] As illustrated in FIG. 36, a generator assembly 57 is also partof the power take off assembly 50. The generator assembly 57 includes amagnet wheel 571 connected to the gear assembly 54, as shown in FIG. 36using suitable fasteners. The generator assembly 57 is a permanentlyexcited 3-phase generator, in which permanent magnets 572, which arefastened to magnet wheel 571, rotate around a stator 573. The stator 573is fixed to the inner side of the power take off lid 59. The locationand arrangement of the generator assembly 57 provides for easyencapsulation because of reduced wiring requirements. The magnet wheel571 rotates around the stationary coils. This arrangement isadvantageous because it eliminates the need for rotating coil membersand also in view of possible repair work. Furthermore, it reduces theweight of the rotating masses. Additionally, the magnet wheel 571 isconstructed as an extrusion-molded part.

[0164] The rotational speed of the crankshaft 123 is measured by anengine or crankshaft speed sensor 58 located within the power take offhousing 59. A cup shaped actuator 544 is secured to the gear assembly 54between the large gear 543 and the magnet wheel 571 of the generatorassembly 57. The actuator 544 extends between the gear 543 and wheel 571and between the sensor 58 and the wheel 571, as shown in FIG. 36. Theactuator 544 includes a plurality of teeth extending around theperimeter thereof. A predetermined number of teeth are missing atpredetermined locations along the perimeter. The sensor 58 detects theabsence of the teeth as the actuator 544 rotates. The speed of thecrankshaft and engine speed can be determined from this.

[0165] Alternatively, it is contemplated that the magnet wheel 571 mayinclude at least one conductor piece mounted therein. The conductorpiece triggers the crankshaft or engine speed sensor 58. Instantaneousvalues of the crankshaft position can be received therefrom and theangular speed (rotational speed) is then calculated by the enginemanagement system 200, described below. The angular resolution is 10°,i.e. during rotation of the crankshaft 123, after every 10° of rotation,a pulse is sent by the crankshaft position sensor to the control device.It is contemplated that the present invention is not limited to anangular resolution of 10°; rather, angular resolutions greater than andless than 10° are considered to be well within the scope of the presentinvention.

[0166] The arrangement of the components within the power take offhousing 59 results in a more compact engine design. As described above,the engine components are located on the power take off end. The powertake off housing 59 protects these elements from the marine conditionsin which the personal watercraft operates. Furthermore, a common driveassembly connected to the crankshaft 123 is provided to drive thesecomponents without the need for numerous belts and other connections.Additional features and benefits of the power take off assembly 50 willbe described below in connection with the description of the lubricatingsystem 60, the blow-by ventilation system 70, engine cooling system 80and supercharger 90.

Lubricating System

[0167] The lubricating system 60 will now be described in greater detailin connection with FIGS. 8, 11, 12, 14-16 and 32-35.

[0168] The engines 1 and 2 have a dry-sump lubricating system 60. Thelubrication system 60 includes the oil tank 11, described above andshown in FIG. 8. The oil collected in the crank chambers 121 emergestherefrom via outlet openings 111 into a channel 112. The oil then flowsto the upper portion 113 of the oil tank 11 adjacent the balance shaft115. From there, the oil flows back by gravity to the bottom of the oiltank 11, where the oil is collected and stored.

[0169] From the oil tank 11, the oil is conveyed to an oil coolingassembly 86, shown in FIGS. 23 and 25, by an oil pump 61, as shown inFIGS. 25 and 33 through integrated channels in the lower crankcase 12.The oil pump 61 is integrated into the power take off housing 59 and iscoaxially disposed and driven by the balance shaft 115 via a connectingshaft 612. The connecting shaft 612 is received within a suitable recesswithin the end of the balance shaft 115 such that rotation movement ofthe balance shaft 115 is transferred to the drive shaft 612. The oilpump 61 is preferably a troichoid pump. It is preferred that the oil besucked from the bottom of the oil tank 11. Furthermore, it is alsopreferred that the oil be removed from a more centrally located pickupposition within the tank 11, rather than the front or rear of the tank11. This is a preventative measure to avoid air entrapment in extremeoperating conditions (extreme acceleration and deceleration modes). Theoil cooling assembly 86 is designed as a plate-type cooler and is fixedonto the cylinder block 10. To cool the engine, water is used in aclosed cooling system 80, described in greater detail below.

[0170] From the oil cooling assembly 86, the oil is conveyed to the oilfilter unit 62, as shown in FIGS. 32 and 34 through integrated channelsin the lower crankcase 12. The oil filter unit 62 has an oil filtercasing 621 that is integrated to the power take off housing 59. The oilfilter unit 62 is closed at one end by a removable oil filter cover 622.Located within the oil filter casing 621 is an annular oil filter 623and a valve rod 624. One end of the valve rod 624 is connected with theoil filter cover 622. The valve rod 624 is secured to the cover by asuitable fastener. The valve rod 624 acts as a fastener to secure thecover 622 to the filter casing 621. The other end of the valve rod 624extends into a drainage opening 625. When the valve rod 624 is pulledout of the drainage opening 625, the oil which has remained in thefilter casing 621 can automatically drain through the drainage opening625. Alternatively, the oil filter cover 622 may be configured as ascrew lid.

[0171] Unlike conventional oil filter units where the overflow valve isintegrated in the upper region of the filter cover 622, the oil filterunit 62 includes an external overflow valve 626 and a bypass duct 627.In the event that the oil filter unit 62 is clogged, a direct connectionis formed between an inlet channel 628 and an outlet channel 629 of theoil filter unit 62. This arrangement has the advantage that the oil doesnot flow around a dirty oil filter. Thus, no dirt particles cancontaminate the oil circuit.

[0172] The filtered oil is then supplied to the engine 1 or 2 forlubricating the various components through the main oil gallery in theupper crankcase 13 of the crankcase 10, as illustrated in the oilcircuit in FIGS. 8 and 11.

[0173] One aspect of the lubricating system 60 relates to the return ofthe oil from the crank chambers 121 in the upper crankcase 12 into theintegrated oil tank 11. The oil is pushed out of the crankcase. This iseffected by a differential pressure acting between the crank chambers121 and the oil tank 11 and the induction system, respectively. Thisdifferential pressure is a result of the pressure pulses caused by thepistons 1241 in the crank chambers 121. It is also partially due to aconsequence of a “Blow-By” effect, which refers to cylinder pressurelosses. The piston 1241 does not provide a 100% sealing on the cylinderwall, so part of the combustion gas caused during combustion leaks pastthe cylinder downwardly into the lower crankcase 12. This so-calledblow-by gas creates additional pressure in the crank chambers 121 belowthe pistons 1241 and is dependent on the load and the rotational speedof the engine. However, on account of the above-mentioned blow-byeffect, the overall effect results in a pressure that is always abovethe pressure between the air box and the throttle body. The return ofthe blow-by gas is described in greater detail below in connection withthe blow-by ventilation system 70.

[0174] The rotational movement of the crankshaft 123 is also utilized tocarry oil to the outlet openings 111, and here two effects are to befound. First, by the direct contact of the crank webs 1231 with the oil,in case of direct wetting, there occurs an entrainment effect as aconsequence of the shearing forces. Second, with smaller amounts of oilin the crank chambers 121, if there is no direct contact between crankweb 1231 and oil, gas forces will occur which likewise drive the oil tothe respective outlet openings 111. At the base of the crank chambers121, in the vicinity of the outlet openings 111, stripper edges may bearranged which strip the oil from the crank webs 1231.

[0175] To enable an optimum utilization of the above-described effectfor the oil return, the three crank chambers 121 (discussed above) inthe crankcase 12 are hermetically separated from each other, and eachcrank chamber 121 is equipped with a separate outlet opening 111 for theoil. Thus, the pressure in one chamber is not affected by the pressurein the other chambers. The cross-sections of the channel system for theoil return following the outlet openings 111 are dimensioned suitably(i.e. not too large) so as to ensure the conveyance of the oil back tothe oil tank 11 on account of the differential pressure, without therisk of a pressure equalization between oil tank 11 and crankcase 12.Alternatively, the channels can also unify, so that one single channel112 leads to the oil tank 11. The arrangement should be designed suchthat no oil “short-circuit” and no pressure balance will occur betweenthe individual crank chambers 121, i.e. oil must not be permitted toflow directly from one crank chamber 121 into another chamber.

[0176] The return channels 112 for the oil return from the threehermetically closed crank chambers 121 to the oil tank 11 may berealized by channels cast into the lower crankcase 12 which enter theoil tank 11 adjacent the union between the upper crankcase 13 and thelower crankcase 12. Alternately, they may be realized by separate ducts,in particular hoses or tubes. As such, normally hoses are only used inconnection with external oil tanks. In the present “in-case oil tank,”hoses can be avoided. To prevent an undesired flow-back of oil from theoil tank 11 to the crank chambers 12 and—in consequence—a flooding ofthe crank chambers in extreme inclined positions or in flip-overposition of the personal watercraft 5, non-return valves (notillustrated) may be installed in the channels 112.

[0177] To remove the lubricating oil which has collected in the regionclose to the bottom of the crank case 12 adjacent the bottom of thepower take off housing 59, a separate suction pump 71 is provided. Likethe oil pump 61, the suction pump 71 is coaxially arranged along anddriven by the balance shaft 115. The pump 71 is preferably a troichoidpump. The pump 71 is located on an opposite end of the balance shaft 115when compared to the pump 61. The oil is conveyed from the bottom of thepower take off housing 59 through a duct 126 cast into the lowercrankcase 12 to the suction pump 71. Alternatively, it is contemplatedthat the blow-by gas created in the crank chamber 121 adjacent the powertake off housing 59 is fed into the power take off housing 59 to providepressure to remove the oil from the bottom of the power take off housing59 near the bottom of the crank case.

[0178] The oil collected in the bottom of each crank chamber 121 exitsthrough the opening 111. The oil is then driven through the channel 112back to the oil tank 11 by the blow-by gas pressure. The oil collectedinside the power take off housing 59 is removed by a suction pump 71 orother suitable pumping assembly. The oil flows through a channel 126,shown in FIGS. 11, 41 and 49, again integrated into the lower crankcase12 from the power take off side to the opposite side, where the suctionpump 71 is mounted, as shown in FIGS. 40 and 41. The oil passes throughan oil sieve 72 before it enters the suction pump 71 and is finallyconveyed back through a U-shaped channel 711 to the oil tank 11, asshown in FIGS. 11, and 40. It is contemplated that the channel 711 isintegrated in the housing of the suction pump 71.

[0179] Regarding the oil circuit, it is added that cooling andlubrication of the pistons 1241 and liners are effected by aid ofspraying nozzles 64 at the lower side of the piston 1241, as shown inFIG. 8. Oil is supplied to the nozzles 64 from the main oil gallery 65.The spray nozzle 64 is positioned such that the jet reaches the pistonlower side not only in the lower dead center position illustrated, butalso in the upper dead center position.

[0180]FIGS. 8 and 35 illustrate one possible oil channel system 63 inthe region of the cylinder head housing 20 by way of a schematic 3Drepresentation. Other systems are contemplated to be well within thescope of the present invention. The oil is conveyed to the cylinder headhousing 20 through at least one ascending duct 631 in the uppercrankcase 13. The ascendind duct 631 is connected to the main oilgallery 65. The oil enters cylinder head housing 20 from the ascendingduct 631 through a transverse bore 632. In the ascending duct 631, athrottle 6311 is installed which restricts the amount of oil flowingtherethrough. In addition, a check valve 6312 is disposed in theascending duct 631, which blocks the oil conduit as soon as the engine 1or 2 is stopped. As such, a certain amount of oil can be stored in thechannels in the cylinder head housing 20. This stored oil isparticularly useful during a cold start since lubrication can beinitiated rapidly therewith and provided to the valve train sooner toprevent damage to the valve train.

[0181] Connecting bores 633 branch off of the transverse bore 632 andconnect the latter with the bores 634. The bores 634 also receive thecylinder head fastening screws. The oil rises upwardly in the annulargap between the cylinder head screw and the corresponding bores 634. Theoil then enters into a V-shaped channel section 635 formed by twoobliquely downwardly directed bores 6351 and 6352. From the ascendingbranch 6352 of the V-shaped channel section 635, the oil directly entersinto the interior of the hollow rocker arm support axle 28. From there,the oil is directed to the bearing places of the rocker arm assemblies25 and 26 via the radial openings 282, as shown in FIG. 14. Also, theoil is admitted to the operating assemblies 253 and 263. It iscontemplated that other channel systems and arrangements are well withinthe scope of the present invention provided the channel systems conductlubricant from the main oil gallery 65 to the support axle 28.

[0182] Lubricant is supplied to the camshaft 29 via bearing bracket 293,described above, through bore 636.

[0183] Below the camshaft 29, the oil may accumulate in a small basin inwhich the lobes 291 and 292 of the camshaft 29 may be immersed forlubricating purposes. The lubricant within the cylinder head housing 20collects in a depression under the camshaft 29 adjacent the cylinderclosest to the power take off assembly 50. The oil from the othercylinders within the cylinder head flows to the depression throughpassageways 295, which interconnect the areas in the cylinder headadjacent the other cylinders. The oil exits the cylinder head housing 20through an inclined passageway into the control chain chamber 202 whereit flows into the power take off assembly 50. This lubricant contributesto the lubrication of the gears and supercharger 90(if present) withinthe power take off assembly 50.

Blow-By Ventilation System

[0184] The engines 1 and 2 are preferably equipped with a blow-byventilation system 70 for separating oil from the vented blow-by gas. Apreferred form of the blow-by ventilation system 70 is illustrated inFIGS. 3, 4, 11, 40, 41 and 46.

[0185] The blow-by gas originating from the combustion chambers 124 dueto leakage between the pistons 1241 and cylinder liners firstaccumulates in the (sealed) crank chambers 121 and from there it flowstogether with the oil through the channels 112 to the oil tank 11, whereit accumulates and mixes in the upper portion 113 of the oil tank 11with any gas in the oil tank 11 from the power take off assembly 50.From the oil tank 11, the gas mixture is then conveyed through a channel712 (in the housing of the suction pump 71 and the lid of the sieve 72),shown in FIG. 40 to a shutoff and pressure relieve valve 731 which isopen in normal engine operation. The pressure relief valve 73 includes avalve rod 731 that moves the valve 73 between open and closed positionsby a solenoid assembly 77. In the event that the solenoid assembly 77 isnot operational, the pressure relief valve 73 includes a spring assembly732 that permits the opening of the valve 73 in the event of a build upof pressure within the tank 11.

[0186] The gas mixture from the oil tank 11 is split into two partialflows: a first portion flows back to the cylinder head chamber withinthe cylinder head housing 20 through a passageway 74, shown in FIGS. 40and 41. A second portion is vented tangentially into an oil separator 75designed as a cyclone. In the cyclone, the gas mixture is separated fromoil by centrifugal forces due to the swirling of the gas/oil mixture inthe cyclone. The cleaned gas mixture leaves the cyclone through acentral pipe 751. The cleaned gas mixture then passes a second shutoffand pressure relief valve 76 and is finally conveyed to the air intakebetween the airbox and the throttle body 411, where it merges with thefresh air drawn in by the engine.

[0187] The shutoff and pressure relief valve 76 is also mounted on thevalve rod 731 and is also actuated by the solenoid 77. With thisarrangement, the valves 73 and 76 operate simultaneously. The valves 73and 76 are closed by drawback springs 732 and 761 when the solenoid 77is not activated and they are open when the solenoid 77 is activated.With this arrangement, the engine is sealed, preventing oil leaks whenthe engine is shut down. In normal (upright vehicle) engine operation,the solenoid 77 is activated and the valves 73 and 76 are openedrespectively. However, in the event of a roll-over of the vehicle, thevalves are closed instantly to prevent oil from entering the inductionsystem 40 and/or the airbox and leaking into the environment. Theclosure of valve 73 prevents oil from accumulating in the cylinder headhousing 20 in a roll-over event. This would cause a temporary lack ofoil in the oil tank 11, when the personal watercraft 5 has returned to anormal upright position and could result in an undersupply of lubricantto the engine, which may result in severe damage to the engine 1 or 2.The valves 73 and 76 are also closed when the engine is shut down.

[0188] A pressure sensor or sensor switch may be provided in the oiltank 11 or in the channel 712 to sense the pressure within the tank 11.If the oil pressure exceeds a certain threshold value, the enginemanagement system 200 operates in an emergency mode (e.g. limp homefunction). The engine management system operates the engine at a reducedspeed. The engine management system also interacts with other onboardcomputers systems to notify the operator of the engine malfunction.Additionally, the pressure sensor can be used to detect oil leakage inthe lubrication circuit.

[0189] The gas mixture enters the upper portion of the cyclone 75through the opening 755. As such, the gas mixture tangentially entersthe cyclone 75. Oil droplets within the gas mixture are thrust againstthe inner wall of the cyclone 75 as a result of centrifugal forceswithin the cyclone 75.

[0190] The separated oil then flows down the inner wall of the cyclone75 towards opening 752; collects in the bottom of the cyclone 75; andexits the cyclone 75 through an opening 752 into a channel 753integrated in the sieve lid 721, and merges with the oil flow from thepower take off assembly 50 in front of the oil sieve 72, to be conveyedback to the oil tank 11. Within the channel 753 there is provided athrottle 754 which ensures that a sufficient height negative pressure(vacuum) can build up in the suction port of the suction pump 71, sothat the power take off housing 50 is drained reliably in all operatingconditions. In a cold start condition (when the oil is very viscous) thethrottle 754 may even be closed by an additional valve (not shown)especially at idling speed to guarantee the aforesaid requirement.

[0191] An oil filler tube 78 is integrated to the cyclone 75. A cap 781is provided for closing the filler tube 78. Fresh oil flows down thefiller tube 78 into a channel 722 integrated in the sieve lid 721. Theoil enters a U-shaped duct through a port 715, shown in FIG. 40, in thehousing of the suction pump, merges with the oil from the power take offassembly 50 and is finally conveyed to the oil tank 11.

[0192] In the preferred embodiment, the valves 73 and 76, the cyclone 75and the oil filler tube 78 are assembled to form a single unit.

[0193] In accordance with the blow-by gas ventilation system 70described herein, a slight vacuum (underpressure, negative pressure,subpressure) is generated in the interior in the power take off assembly50 and within the cylinder head housing 20. As a result, no oil orcontaminated blow-by gas can escape to the environment.

Engine Cooling System

[0194] An engine cooling system 80 will now be described in connectionwith FIGS. 25, 32 and 33. The engine cooling system 80 is a closedsystem utilizing a coolant such as glycol, water or a mixture of them.The present invention, however, is not limited to these coolants;rather, it is contemplated that other cooling liquids are considered tobe well within the scope of the present invention. The cooling circuitof the engine cooling system 80 is illustrated in FIG. 25. The closedloop cooling system 80 cooperates with the open loop cooling arrangementdescribed above in connection with the exhaust manifold 30 toeffectively cool the engines 1 and 2.

[0195] The engine cooling system 80 includes a pump assembly 81 locatedon one end of the engine 1 or 2, as shown in FIG. 32.

[0196] As illustrated in FIG. 33, the pump assembly 81 is arrangedexternally of the power take off housing 59. The power take off housing59 and pump lid 611 together form the pump casing. It is designed as arotary pump and consists of an impeller 811 which is located, screwed orattached onto the end of the connecting shaft 612, which projects fromthe power take off housing 59. The connecting rod 612 also drives theoil pump 61. Impeller 811 is driven by connecting rod 612. Theconnecting rod 612 also drives the oil pump 61. The pump assembly 81also includes a pump lid 812, which is fastened to the power take offhousing 59 and forms the pump casing in cooperation therewith. The pumpassembly 81 has a one piece housing having an integrated thermostat.

[0197] As shown in FIG. 25, the coolant flows from the pump assembly 81through a passageway 82 to the cylinder block of the upper crankcase 13.The passageway 82 includes a main passageway 821 and a by-passpassageway 822. The passageways 821 and 822 direct coolant to thecooling passageway 125 in the cylinder block. The coolant flows alongthe exterior of the cylinders 124, as shown in FIG. 25. With thisarrangement, the coolant travels in a generally U-shaped manner along aside of the cylinders 124 adjacent the intake manifold; around the endof the cylinder furthest from the power take off assembly 50 and thenalong the side of the cylinders adjacent the exhaust manifold in adirection back towards the power take off assembly 50. At the same time,the coolant is directed in an upward direction towards the cylinder headhousing 20. The by-pass passageway 822 reduces the load on the mainpassageway 821 and improves the flow pattern in the cooling passageway125 at an end portion of the cooling passageway 125 opposite the inlet.The coolant from the by-pass passageway 822 mixtures with the coolant inthe coolant passageway 125 to reduce the temperature of the coolant inthe end portion of the cooling passageway 125. Furthermore, the entry ofcoolant into the cooling passageway 125 from the by-pass passageway 822improves the upward flow of coolant into the cylinder head housing 20.It is preferred that the passageways 821 and 822 are integrally formedin the power take off housing 59 and crankcase 10. It, however, iscontemplated that the passageways may be hoses connecting the componentsto one another.

[0198] From the upper crankcase 13, the coolant then passes upwardly tothe cylinder head housing 20 through bores 131 in a head gasket 130positioned between the upper crankcase 13 and cylinder head housing 20,as schematically illustrated in FIG. 25. The bores 131 are located onthe exhaust manifold side of the gasket 130. These bores 130 act asthrottles to adjust the flow of coolant into the cylinder head housing20. Additional small bores are located on the intake manifold side ofthe gasket 130. These bores vent air trapped within the passageway 125into the cylinder head housing 20. The coolant first passes over theexhaust side of the cylinder head toward the intake side of the cylinderhead before exiting the cylinder head housing 20 through a commonpassageway.

[0199] From the cylinder head housing 20, the coolant is then conveyedthrough a hose to a thermostat 83 through an inlet passageway 817located on the pump assembly 81, as shown in FIGS. 25 and 32. Asillustrated in FIG. 33, the thermostat 83 is directly mounted on thepump lid 812. The thermostat 83 comprises a two-part thermostat casing831 and 832 including hose connections and a temperature-sensitive valve833, which automatically opens if a predetermined temperature thresholdvalue is exceeded. The coolant then flows through outlet passage 816 toa heat exchanger 84 (shown schematically in FIG. 25), where the coolantis cooled by exchanging heat to the atmosphere. This can be in the formof a cooling plate exposed to the body of water. The cooling plate maybe located in a lower portion of the hull of the personal watercraft S.The cooling plate is described in U.S. Provisional patent applicationSer. No. 60/160,819, filed Oct. 21, 1999 entitled “WATERCRAFT WITHCLOSED-LOOP HEAT EXCHANGER,” and U.S. patent Application Ser. No.09/691,129, filed Oct. 19, 2000 entitled “WATERCRAFT HAVING A CLOSEDCOOLANT CIRCULATING SYSTEM WITH A HEAT EXCHANGER THAT CONSTITUTES ANEXTERIOR SURFACE OF THE HULL” the specifications of which areincorporated herein specifically by reference. The coolant is thenreturned to the pump assembly 81 through an inlet 815.

[0200] The primary purpose of the cooling system 80 is to cool theengine 1 or 2 during operation. The operation of the cooling system 80is temporarily modified during engine start-up so that the enginequickly reaches an optimal operating temperature. During initial enginestart-up, the thermostat 83 deactivates the heat exchanger 84. As such,the coolant is not cooled prior to reentry into the pump assembly 81;rather, the coolant returns directly from the inlet 817 into the coolantpump 81.

[0201] The cooling system 80 furthermore includes an oil coolingassembly 86. The oil cooling assembly 86 is connected to pump assembly81 and thermostat 83. With this arrangement, a portion of the coolantfrom the pump assembly 81 is directed to the oil cooling assembly 86through passageway 861 to cool the engine oil. After passing through theoil cooling assembly 86, the coolant returns to the thermostat 83 viareturn passageway 862. The coolant from the passageway 862 enters thethermostat housing in the vicinity of the inlet 817. The oil coolingassembly 86 preferably is a plate-type cooler and disposed on the sideof the lower crankcase 12. The coolant, which heats sooner than the oil,is used to heat the engine oil during engine start-up.

[0202] The cooling system 80 further includes a temperature sensor 87,which is linked to the engine management system, shown in FIGS. 25 and42. As shown in FIG. 25, an expansion reservoir 88 is provided in thereturn from the cylinder head housing 20 to the thermostat 83, as shownin FIG. 23. The expansion reservoir 88 adjusts for expansion of thecooling fluid within the system 80. The expansion reservoir 88 further arefill port 881 for refilling the system 80. The reservoir 88 furtherprovides a venting function for removing air from the cooling system 80.In this manner, the interconnecting duct between the reservoir 88 andthe cylinder head housing 20 has to be linked to the highest point inthe cylinder head housing 20 to prevent the formation of an air barrierwhich could cause overheating.

Supercharger Assembly

[0203] As discussed above, the engines in accordance with the presentinvention may include a supercharger 90. The engine 2 having asupercharger 90 is illustrated in FIGS. 6, 7, 30, 31 and 38. Thesupercharger 90 is provided to increase the air intake and enhanceengine performance. The preassembled supercharger 90 is plugged in acorresponding port 591, as shown in FIG. 33, in the power take offhousing 59 and sealed with sealing rings 592, as shown in FIG. 38. It iscontemplated that a turbocharger may be used in connection with thepresent invention. The supercharger, however, provides improvedoperating characteristics when compared to the turbocharger.Furthermore, the turbocharger produces additional heat as compared tothe supercharger, which places increased demands on the cooling systems.

[0204] The supercharger 90 includes a cast housing 91, which ispreferably formed from a metal, however, it may be formed from a highstrength plastic or other suitable material. The housing 91 includes aninlet portion 911. The inlet portion 911 is operatively connected to theairbox (not shown). Air enters the supercharger 90 through the inletportion 911. Located within the housing 91 adjacent the inlet portion911 is an impeller 92, which operates to draw air into the superchargerfrom the airbox. An air passageway 912 extends around the impeller 92 tocollect the air compressed by the impeller. The air passageway 912 isconnected to the intake manifold 41 through the throttle body 411. Thehousing 91 further includes a mounting portion 913 that extends backwardfrom the inlet portion 911. The mounting portion 913 is received withinthe port 591 in the power take off housing 59 and sealed with at leastone sealing assembly 592.

[0205] As shown in FIG. 38, a blower drive shaft 922 extends through themounting portion 913 and inlet portion 911. The blower drive shaft 922is rotatably mounted within the housing 91 with at least one bearingassembly 921. A drive pinion 93 is coupled to the blower drive shaft922. It is preferred that this be a non-positive coupling. As such, thedrive pinion 93 is non-positively connected with the blower shaft 922via an intermediate element 94 by a biasing spring force, which ispreferably supplied by a spring assembly 95. The spring assembly 95includes a plurality of cup springs. Other spring assemblies and meansfor providing a connection that can slip under high torque to preventdamage to the impeller or other components, however, are considered tobe well within the scope of the present invention. The drive shaft 922includes splines to prevent rotational movement of the intermediateelement 94 with respect to the drive shaft 922. The shaft 922 includes alubrication passageway that delivers lubricant to the drive pinion 93 toreduce wear. The lubrication passageway is connected to the lubricationsystem. The connection between the drive pinion 93 and the intermediateelement 94 is formed as a plane frictional surface. This uniqueconnection assembly can dampen the rotational and torsional vibrationstransmitted by the crankshaft 123.

[0206] The supercharger 90 is operatively coupled by the drive pinion 93to the gear assembly 54 through gear 5431. The supercharger 90preferably includes a cooling jacket connected to the open or closedloop cooling system to cool and prevent failure of the supercharger 90.The cooling of the supercharger 90 improves engine performance.

[0207] In accordance with the present invention, the supercharger 90preferably utilizes a low-cost rotary (radial or radial-axial) blower.The present invention, however, is not limited to these blowers; rather,it is contemplated that a positive displacement blower (e.g. a Rootes orWankel blower) may be employed. Furthermore, the supercharger 90 may beused for separating a certain water content from the intake air.

Control Tensioner

[0208] In accordance with the present invention, the engines 1 and 2 arepreferably equipped with a control tensioner for controlling the tensionwithin chain 55. The present invention, however, is not limited for usewith a chain; rather, it is contemplated that the control tensioner canbe used with other flexible linkages, including but not limited tobelts. A mechanical chain tensioner 100 is illustrated in FIG. 39. Thetensioner 100 includes a driving element 101. The driving element 101preferably includes a spring assembly. The spring assembly is preferablya rotationally active helical pressure spring. The spring assembly 101is rotationally biased by aid of a thread cap 102. The spring includes aspring ender 1011 that engages a slot 1021 in thread cap 102. The threadcap 102 is externally screwed into a retainer 103. The spring assembly101 is received at one end in a blind hole bore of a hollow adjustmentelement 104 which is screwed into a thread bore of the retainer 103. Thespring also includes a spring end 1012 that engages a slot 1042 inadjustment element 104. The overlapping thread engagement of adjustmentelement 104 with retainer 103 is designed to be relatively long. As oilgets into this threaded connection, it provides a small damping effectto the adjustment element 104 due to vibrations of the cam chain. Thissmall damping effect is enhanced if the thread overlap is keptrelatively long. The external thread of the adjustment element 104preferably includes multiple threads and it is designed such that it isborderline self-locking in the retainer 103. This design must take intoaccount the presence of oil between the threads, which reduces friction,when determining the necessary inclination of the threads. If theinclination is too small (very self locking), a strong spring force isrequired to overcome the locking action of the threads. It is desirableto avoid unnecessary tension on the chain to avoid wear and decreases inthe lifetime of the chain. The self tensioning action is effected by theinteraction of the chain vibration and the borderline self locking ofthe threads. That is, it will maintain its extended position undernormal loads but can retract a distance under high loads to preventdamage to the cam chain. For instance, if automatic adjustment occurswhen the engine is cold, upon reaching operation temperature, thealuminum cylinder and head have expanded more than the steel cam chainand can create too high of a tension in the chain. The borderline selflocking feature allows the plunger to retract slightly before chaintension becomes so high as to damage the chain. The adjustment element104 is rotationally driven by the spring assembly 101 if the tension ofthe chain 55 slackens and is axially outwardly displaced. The adjustmentelement 104 acts via a balancing arcuate intermediate piece 105 on atensioning rail 106. The chain tensioner 100 enables a later adjustmentby aid of the combined biasing and fixing element 102 if the chain 55undergoes elongation.

[0209] The thread piece 102, the retainer 103 and adjustment element 104preferably are made of synthetic material because of the smaller thermalelongation encountered as compared to aluminum. The adjustment element104 includes a steel insert 1041 on one end to reduce wear.

[0210] In accordance with the present invention, the engines 1 and 2described herein are not limited to the mechanical chain tensioner 100;rather, other tensioner assemblies are contemplated to be well withinthe scope of the present invention. For example, a hydraulic tensionermay be used. The mechanical tensioner 100, however, has numerousadvantages over this hydraulic counterpart. First, the mechanicaltensioner 100 can be manufactured at a lower cost and does not require acomplicated oil supply.

Engine Control Unit

[0211] The operation of the engine 1 or 2 is controlled by an enginemanagement system 200, as shown in FIG. 42. The engine management system200 includes an electronic control unit 201 monitors and controls theoperation of various engine components including but not limited toignition, the fuel pump, the fuel injection assembly, the air intake,engine cooling, engine speed, engine lubrication, exhaust gas in themuffler in response to input from various sensors and monitors locatedwith the engines 1 and 2. It is contemplated that the electronic controlunit 201 may further control functions, such as, e.g., realization of adeparting lock, realization of a start/stop control, and theidentification of authorized personal watercraft users. The electroniccontrol unit 201 further communicates with the other computer systems onthe personal watercraft for the control of instruments, non enginewatercraft functions and service needs.

[0212] The engine management system 200 also controls the gas pump 203in the gas tank 204, which includes a coarse filter 2041 and a floatassembly 2042.

[0213] The gas pump 203 has an associated pressure regulator 2043, suchthat a constant gas pressure is mechanically provided. From there, areturnless fuel system 205 leads to the injection nozzles or valves 434seated on the fuel rail 431. These injection nozzles 434 inject the fuelin the form of jets in the air in the intake passageway. The enginemanagement system 200 controls the operation of the nozzles 434 suchthat there is sequential injection, wherein each cylinder has anindividual injection (i.e., no group injection). The injection amount isdetermined by the engine control device 201 on the basis of the appliedcharacteristic fields by the pulse width, i.e. by the duration of theinjection time.

[0214] A returnless fuel system 205 prevents the fuel from heating dueto the engine heat, as could otherwise be the case with a fuel returnfrom the engine to the fuel tank.

[0215] The engine management system 200 also includes various sensors,such as the temperature sensor 39 in the exhaust muffler, an airtemperature sensor 43 attached to the intake manifold 41 and a watertemperature sensor 87.

[0216] A knock sensor 206 senses at an early time the knocking criticalfor the engine—which has a high specific performance level. The knocksensor 206 includes a piezo quartz element, which measures thesolid-borne acoustic signals at the cylinder block and transmits thecorresponding signals to the electronic control unit 201. The latter hasa detection software to detect a possible knocking combustion and tocause a correction in a manner known per se, by ignition angledisplacement.

[0217] The sensors further include the crankshaft position sensor 207. Acorresponding rotary position sensor 208 is associated with thecamshaft. By aid of this camshaft sensor 208, it is recognized whetherthe crankshaft is present in the angle range of 0 to 360° or in therange of 360 to 720°, which is possible via the camshaft because thelatter rotates at half the rotational speed of the crankshaft. For thesake of simplicity, the camshaft sensor 208 is directly associated withthe chain wheel 551 at the camshaft.

[0218] For load measurement, the actual load of the engine is calculatedby the intake manifold pressure measured by sensor 210 and engine speedmeasured from the crankshaft 123 in the power take off assembly 50. Athrottle potentiometer 209 is used for corrections and a limp homefunction. In the event the engine is operating in a limp home function(e.g., broken intake air pressure sensor), the engine control unit 201communicates with another onboard computer system to notify the operatorvia an instrument panel that the engine is operating in a limp homefunction. A pressure sensor 210 is arranged in the suction pipe to sensethe absolute pressure, which is especially useful for the engine 2containing the supercharger assembly 90 and for all operation modes withslightly opened or closed throttle valve. Thus, there is no direct airamount or air mass measurement, but auxiliary parameters are usedtherefor.

[0219] Finally, for the sake of completeness, various voltage checksshould be mentioned which are carried out by the electronic control unit201, e.g. for the supply voltage of the injection valves, which isuseful insofar as the board voltage on the personal watercraft 5 mayvery well fluctuate.

[0220] It will be apparent to those skilled in the art that variousmodifications and variations may be made without departing from thescope of the present invention. Thus, it is intended that the presentinvention covers the modifications and variations of the invention,provided they come within the scope of the appended claims and theirequivalents.

What is claimed is:
 1. A four stroke internal combustion engine,comprising: a crankcase; a cylinder head connected to the crankcase,wherein the crankcase and the cylinder head form at least one cylinder;at least one intake valve for the at least one cylinder; at least oneexhaust valve for the at least one cylinder; a valve actuation assemblylocated in the cylinder head for operating the at least one intake valveand the at least one exhaust valve; at least one air intake passagewayoperatively coupled to the at least one cylinder through the at leastone intake valve; and an air intake system connected to the cylinderhead and operatively connected to the at least one air intakepassageway, the air intake system comprising an air intake manifoldhaving a central air passageway extending between a first end and asecond end and at least one passageway extending from the central airpassageway to a free end, wherein the air intake manifold has agenerally symmetrical construction, and wherein the free end of the atleast one passageway is operatively connected to the at least one airintake passageway.
 2. The four stroke internal combustion engineaccording to claim 1 , wherein the air intake manifold comprising; afirst opening in the first end; a second opening in the second end; andan end cap located in one of the first opening and the second opening.3. The four stroke internal combustion engine according to claim 2 ,wherein the engine is a normally aspirated engine, wherein the airintake system further comprising: an air inlet located at the firstopening of the air intake manifold, wherein the end cap is located inthe second opening.
 4. The four stroke internal combustion engineaccording to claim 3 , wherein the air intake system further comprises:a throttle connected to the air inlet to regulate the flow of air intothe air intake manifold.
 5. The four stroke internal combustion engineaccording to claim 4 , wherein the throttle includes an idle by-pass,wherein a predetermined supply of air is supplied to the air intakesystem through the idle by-pass when the engine is operating in an idleoperating condition.
 6. The four stroke internal combustion engineaccording to claim 2 , further comprising: a supercharger operativelyconnected to the air intake system, an air inlet located at the secondopening of the air intake manifold, wherein the supercharger isoperatively connected to the air intake manifold through the air inlet,wherein the end cap is located in the first opening.
 7. The four strokeinternal combustion engine according to claim 6 , wherein the air intakesystem further comprises: a throttle connected to the air inlet toregulate the flow of air from the supercharger into the air intakemanifold.
 8. The four stroke internal combustion engine according toclaim 7 , wherein the throttle includes an idle by-pass, wherein apredetermined supply of air is supplied to the air intake system throughthe idle by-pass when the engine is operating in an idle operatingcondition.
 9. The four stroke internal combustion engine according toclaim 1 , wherein the air intake system further comprising: a fuelinjection system operatively coupled to the at least one passagewayadjacent the free end.
 10. The four stroke internal combustion engineaccording to claim 9 , wherein the fuel injection system comprises: acommon fuel rail extending along a top portion of the air intakemanifold; and at least one fuel injection nozzle extending from thecommon fuel rail to the at least one passageway adjacent the free end,wherein the injection nozzle injects fuel into air within thepassageway.
 11. The four stroke internal combustion engine according toclaim 10 , further comprising: an engine control system to which the atleast one fuel injection nozzle is operatively connected, wherein theengine control system monitors engine operating parameters and operatesthe fuel injection nozzle in response to the engine operating parametersincluding at least engine operating speed.
 12. The four stroke internalcombustion engine according to claim 10 , wherein the common fuel railis operatively connected to a returnless fuel supply system.
 13. Thefour stroke internal combustion engine according to claim 1 , furthercomprising: an engine cooling system, wherein the air intake manifoldincludes a cooling jacket operatively connected to the engine coolingsystem.
 14. The four stroke internal combustion engine according toclaim 13 , wherein the engine cooling system comprising: a closed loopcooling system for cooling at least a portion of the engine having atleast one coolant passageway extending around a portion of the at leastone cylinder, wherein the coolant passageway is adapted to containcoolant to remove heat generated by the cylinder during operation; andan open loop cooling system for cooling at least a portion of theengine.
 15. The four stroke internal combustion engine according toclaim 14 , wherein the cooling jacket is operatively connected to theopen loop cooling system.
 16. An air intake system for an engine,comprising: an air intake manifold having a central air passagewayextending between a first end and a second end and at least onepassageway extending from the central air passageway to a free end,wherein the free end of the at least one passageway is adapted to beconnected to the at least one air intake passageway; an air inletconnected to one of the first opening and the second opening; a throttleconnected to the air inlet, wherein the throttle regulates the flow ofair into the air intake manifold; and an end cap secured to another ofthe first opening and the second opening.
 17. The air intake systemaccording to claim 16 , wherein the engine is a normally aspiratedengine, wherein the air inlet is connected to the first opening of theair intake manifold, wherein the end cap is located in the secondopening.
 18. The air intake system according to claim 17 , wherein thethrottle includes an idle by-pass, wherein a predetermined supply of airis supplied to the air intake system through the idle by-pass when theengine is operating in an idle operating condition.
 19. The air intakesystem according to claim 16 , wherein the engine includes asupercharger, wherein the air inlet is connected to the second openingof the air intake manifold, wherein the end cap is connected to thefirst opening, and wherein the supercharger is operatively connected tothe air intake manifold through the throttle.
 20. The air intake systemaccording to claim 19 , wherein the throttle includes an idle by-pass,wherein a reduced supply of air is supplied to the air intake systemthrough the idle by-pass when the engine is operating in an idleoperating condition.
 21. The air intake system according to claim 16 ,wherein the air intake manifold includes a cooling jacket adapted to beoperatively connected to an engine cooling system.
 22. The air intakesystem according to claim 16 , further comprising: a flame arresterpositioned between the first end and the second end within the airintake manifold.
 23. A personal watercraft for use by at least onepassenger, comprising: a hull; a seating assembly for the at least onepassenger; and a four stroke internal combustion engine located withinthe hull, wherein the engine comprises a crankcase secured to the hull;a cylinder head connected to the crankcase, wherein the crankcase andthe cylinder head form at least one cylinder; at least one intake valvefor the at least one cylinder; at least one exhaust valve for the atleast one cylinder; a valve actuation assembly located in the cylinderhead for operating the at least one intake valve and the at least oneexhaust valve; at least one air intake passageway operatively coupled tothe at least one cylinder through the at least one intake valve; and anair intake system connected to the cylinder head and operativelyconnected to the at least one air intake passageway, the air intakesystem comprising an air intake manifold having a central air passagewayextending between a first end and a second end and at least onepassageway extending from the central air passageway to a free end,wherein the air intake manifold has a generally symmetricalconstruction, and wherein the free end of the at least one passageway isoperatively connected to the at least one air intake passageway.
 24. Thepersonal watercraft according to claim 23 , wherein the air intakemanifold comprising; a first opening in the first end; a second openingin the second end; and an end cap located in one of the first openingand the second opening.
 25. The personal watercraft according to claim24 , wherein the engine is a normally aspirated engine, wherein the airintake system further comprising: an air inlet located at the firstopening of the air intake manifold, wherein the end cap is located inthe second opening.
 26. The personal watercraft according to claim 25 ,wherein the air intake system further comprises: a throttle connected tothe air inlet to regulate the flow of air into the air intake manifold.27. The personal watercraft according to claim 26 , wherein the throttleincludes an idle by-pass, wherein a predetermined supply of air issupplied to the air intake system through the idle by-pass when theengine is operating in an idle operating condition.
 28. The personalwatercraft according to claim 24 , further comprising: a superchargeroperatively connected to the air intake system, an air inlet located atthe second opening of the air intake manifold, wherein the superchargeris operatively connected to the air intake manifold through the airinlet, wherein the end cap is located in the first opening.
 29. Thepersonal watercraft according to claim 28 , wherein the air intakesystem further comprises: a throttle connected to the air inlet toregulate the flow of air from the supercharger into the air intakemanifold.
 30. The personal watercraft according to claim 29 , whereinthe throttle includes an idle by-pass, wherein a predetermined supply ofair is supplied to the air intake system through the idle by-pass whenthe engine is operating in an idle operating condition.
 31. The personalwatercraft according to claim 23 , wherein the air intake system furthercomprising: a fuel injection system operatively coupled to the at leastone passageway adjacent the free end.
 32. The personal watercraftaccording to claim 31 , wherein the fuel injection system comprises: acommon fuel rail extending along a top portion of the air intakemanifold; and at least one fuel injection nozzle extending from thecommon fuel rail to the at least one passageway adjacent the free end,wherein the injection nozzle injects fuel into air within thepassageway.
 33. The personal watercraft according to claim 32 , furthercomprising: an engine control system to which the at least one fuelinjection nozzle is operatively connected, wherein the engine controlsystem monitors engine operating parameters and operates the fuelinjection nozzle in response to the engine operating parametersincluding at least engine operating speed.
 34. The personal watercraftaccording to claim 32 , wherein the common fuel rail is operativelyconnected to a returnless fuel supply system.
 35. The personalwatercraft according to claim 23 , further comprising: an engine coolingsystem, wherein the air intake manifold includes a cooling jacketoperatively connected to the engine cooling system.
 36. The personalwatercraft according to claim 35 , wherein the engine cooling systemcomprising: a closed loop cooling system for cooling at least a portionof the engine having at least one coolant passageway extending around aportion of the at least one cylinder, wherein the coolant passageway isadapted to contain coolant to remove heat generated by the cylinderduring operation; and an open loop cooling system for cooling at least aportion of the engine.
 37. The personal watercraft according to claim 36, wherein the cooling jacket is operatively connected to the open loopcooling system.
 38. The personal watercraft according to claim 24 ,further comprising: a flame arrester positioned between the first endand the second end within the air intake manifold.